We live alongside people whose behaviour corrodes everything it touches. The colleague who undermines you while smiling. The partner who makes you question your own sanity. The boss whose cruelty radiates through an entire organisation and follows employees home. For decades, psychology has tried to understand these individuals through the lens of what researchers call the dark tetrad — psychopathy, narcissism, Machiavellianism, and sadism — a cluster of overlapping personality traits marked by callousness, manipulation, and chronic hostility toward others. The science tells us that while only a small percentage of people reach clinical extremes, these traits exist on a spectrum — present in all of us to varying degrees, and capable of causing disproportionate harm when elevated. One person with a high psychopathy score, placed in a position of power, can reshape the behaviour and wellbeing of everyone around them. The effects do not stay at work, at home, or in any one relationship. They spread — what researchers now call a ‘trickle-down darkness’.
Dr Leanne ten Brinke is an award-winning researcher and associate professor at the University of British Columbia, where she directs the Truth and Trust Lab. Over more than two decades of research, she has studied dark personalities in settings as varied as prisons, schools, financial boardrooms, and the United States Senate — examining behaviour from the merely difficult to the genuinely deadly. Her work on deception, distrust, and psychopathic personality has been featured in The New York Times, the Financial Times, the Harvard Business Review, the BBC, and NPR. Her landmark book, Poisonous People: Psychopathy, Narcissism, Manipulation, Sadism — How to Resist Them and Improve Your Life, published by Simon & Schuster in March 2026, weaves together pathbreaking research and deeply human storytelling to give readers evidence-based tools to identify dark personalities, understand how they cause harm, and — critically — get out of toxic situations with as little damage as possible.
I spoke with Dr ten Brinke about what the science really tells us about the people who hurt us, why we so often fail to see the warning signs, how dark traits spread through organisations and families, and how to protect ourselves — and the people we love — from the cost of staying too long.
Q: We tend to think we would recognise a toxic personality. Your research suggests we are actually quite poor at this — especially with the people closest to us. Why?
The research suggests that we are actually reasonably good at detecting dark traits over time — accuracy does genuinely improve with more exposure. But our first impressions can be quite unstable. And this is especially true because people with dark personalities tend to engage in active impression management. If they want something from you — including a close personal relationship — they are not held back by care, compassion, concern, or remorse. They are very willing to lie to get what they want. So our first impressions can be quite deceiving. They can get past that initial filter.
Over time, personality does reveal itself. Take narcissism as an example. Research in small group settings shows that people high in narcissism seem really likeable, confident, and smart at the outset — in that first meeting, you think: that person has all the answers. But over time, they become very unlikeable. The true colours do emerge. The problem is what happens in the window in between — and how far down the road we can already be when they do.
When we are in intimate relationships, we are wired for commitment. We move forward, we start to feel those sunk costs, and we can keep moving forward even after that first impression has started to wear away. We might wonder whether it is something we ourselves are doing that is making the relationship go wrong. We get all kinds of contradictory evidence and continue to question ourselves rather than the other person. And we might get quite far down the road — financially, emotionally, in terms of shared children, shared property, shared social circles — before it genuinely becomes difficult to leave. We are wired to stay in relationships. That is not a flaw; it is a feature. But for people with dark personalities, it is one of the most powerful tools they have.
Q: Can you describe what the dark tetrad consists of — and is it true that all of us carry some of these traits to varying degrees?
The dark tetrad consists of four traits: psychopathy, Machiavellianism, narcissism, and sadism. It started as a triad — sadism was added more recently. If you think of them like a Venn diagram, they all overlap at the same core: callousness, manipulation, and a kind of antagonism or hostility toward other people. But each also has its own distinct flavour.
Psychopathy tends to be associated with impulsivity and rule-breaking. Narcissism — most people have a sense of this — involves grandiosity and a strong self-focus. Machiavellianism is more strategic: these people tend to be calculating, and they use manipulation deliberately in the pursuit of power in particular. And sadism, the most recent addition, describes people who experience genuine pleasure in other people’s pain. That’s the distinguishing feature: it’s not just indifference to your suffering — it’s enjoyment of it.
Now, these are not black-and-white categories. They are personality traits, much like extroversion or openness to experience — things we know exist on a continuum from very low to very high. About 1% of people might meet the clinical criteria for psychopathy, and somewhere between 2% and 5% for narcissistic personality disorder. Truly extreme levels are quite rare. But the traits themselves exist in all of us, and that means everyone has the opportunity — and arguably the responsibility — to understand where they sit. We tend to look outward and identify these traits in others. We tend not to look inward and recognise that we may carry some level of them ourselves. And we can all work on tamping those traits down if we want to live in a more honest and cooperative world.
Q: Why do we so often confuse dark traits with competence — particularly in leadership settings?
There is a great deal of research on the confusion between confidence and competence, and it’s one of the most important traps to understand. Confidence is something that can be projected very quickly. You walk into a job interview, you sound steady, you carry yourself with a kind of broad-shouldered authority, and people presume that this projected confidence means you actually possess the ability you’re claiming. Whereas competence is your real capacity to do those things — which is much harder to fake over time, but also much harder to evaluate in a brief interaction.
We have what’s called a truth bias — a deep-seated tendency to believe the things people tell us. If someone tells us they’re exceptional at something, we tend to believe them. And people with high levels of narcissism or psychopathy are often extraordinarily good at projecting exactly that kind of surface confidence in precisely the critical early window when you’re forming your evaluation of them.
The paradox is that the traits we would not consciously choose in a leader — the lack of empathy, the willingness to bend or break rules, the unflinching self-promotion — are precisely the ones that tend to be mistaken for strength, decisiveness, and vision. We know, logically, that we would not want someone who scores very highly on the dark tetrad in a position of authority over us. And yet sometimes those are exactly the traits that get someone into that position.
Q: You write about a ‘contagion effect’ — the idea that one dark personality in a system reshapes the behaviour of everyone around them. How does that actually work in practice?
This is something I think is really important and something we should be on guard for. If you’ve got one dark personality in an organisation, a family, or a friendship group, the effect does not just stay with them, and it does not just affect the one person they’re directly targeting. It spreads. There is a kind of trickle-down darkness.
There is compelling research showing that if you have a boss with relatively high levels of psychopathic traits at work, those bosses are significantly more likely to bully their subordinates. That leads to enormous levels of stress among the people working under them, and to higher rates of turnover over time. But that stress doesn’t just stay in the office. We get in our car, we get on the subway, we bring it home with us. Research actually shows that having a high-psychopathy boss is associated with more conflict at home. You end up taking the frustration out on your spouse, your children, whoever is around when you get there. The person experiencing that is not even the direct target of the dark personality’s behaviour — they are simply absorbing the stress at secondhand and passing it on.
That is how one individual at the top of a hierarchy can corrode the wellbeing of an entire organisation — and every family that organisation’s employees go home to. The cost of a single toxic personality is never contained to that one personality. It radiates outward in ways that are difficult to trace back to the source, which is part of what makes it so insidious.
Q: Is there a risk that greater self-awareness or empathy actually makes us more vulnerable — that by trying harder to understand a poisonous person, we expose ourselves further?
It depends on what kind of self-awareness and empathy we’re talking about. If your self-awareness is really just projecting who you are onto other people — assuming that everyone thinks, feels, and is motivated the way you are — and you happen to have low levels of these dark traits yourself, then yes, you are probably setting yourself up for difficulty. You will keep expecting them to respond with the same care and concern you’d feel in their position, and they simply won’t.
But ideally, self-awareness includes the recognition that you and other people are genuinely different — that other people have different emotional reactions, different goals, different internal worlds. And this is where what psychologists call cognitive empathy — the ability to understand what someone else is thinking without necessarily being swept up by it — becomes genuinely protective rather than harmful. You can use that cognitive empathy to understand what a dark personality is actually after, how they are likely to behave, what they want from you. That understanding is a tool, not a vulnerability.
There’s also an interesting body of research on what are called guilt-prone people — which you can think of as something like the opposite of a dark personality. Instead of having very low guilt, they have very high guilt. And research suggests they actually make particularly good leaders, because they are very good at taking other people’s perspectives into account and helping to resolve conflict. The moral sensitivity that makes you empathetic is not the same thing as naivety. What matters is how you use it.
I also try to make the case in the book for a degree of compassion and understanding toward people with these traits — because they didn’t choose to be this way. Especially for children who show high levels of these traits early in their lives, that is actually a window where meaningful intervention is most possible, where we can make real changes before patterns become deeply entrenched. But it requires us to care enough about those children to help them, rather than simply writing them off.
Q: Can people with dark traits genuinely change? If we stay in these relationships hoping they will, are we being rational?
What we know from research is that people with high levels of these dark traits tend not to be particularly motivated to change. From their perspective, they’re often getting what they want. The harm they are causing doesn’t register for them the way it registers for you — they don’t have the same level of empathy or concern for others. It is, as I describe it, more of a ‘you problem’ than a ‘them problem’: you have a problem with their behaviour, but they don’t share that evaluation. Why would they want to change something that is, from where they sit, working perfectly well?
So if you are staying, hoping and believing that they will change — especially if you believe that your love, your investment, your patience, is what is going to bring that change about — the research says you should think carefully about that assumption. What you can’t count on doing is changing them. That said — and this matters — if they are motivated to change, research suggests that treatment can help. It can mute some of the harm. Most of this research has been done with incarcerated populations, looking at re-offending rates, and what we find is that if people stick with treatment, re-offending rates do come down. That’s genuinely good news, because the perception out there that change is simply impossible for these individuals is not quite accurate. But it’s more muted harm than a personality transformation. And the motivation to change has to come from within them — not from you.
Q: How do we detect poisonous people earlier? What concrete signals should we be looking for?
The scientist in me says: use structured judgements rather than vibes. Going on the basis of a consistent set of research-backed criteria will give you better results than gut instinct alone — especially because our gut instinct is precisely what dark personalities tend to target and manipulate.
Even after a relatively short interaction, there are behavioural signals worth attending to. People with high levels of narcissism tend to talk about themselves a great deal — the conversation has a way of always circling back to them. People with high levels of psychopathy might be more likely to interrupt you freely while resisting being interrupted themselves. They may try to bait you into arguments, and they tend to push on boundaries — personal and professional — testing where the limits are. One finding from our own research that I think is particularly striking: people with high levels of psychopathy tended to say angry or hostile things while smiling — a strange, unsettling mismatch between what they were saying and how they were presenting physically.
None of these signals alone is definitive. We have all interrupted someone, or talked too much about ourselves at some point. The key is pattern and frequency. Dark personalities do these things more often, more consistently, and in a wider range of contexts than someone who simply had a bad day. Treat your understanding of a new person as a running theory. Gather data over time, in different situations, before committing. Don’t wrap up your evaluation too quickly.
And watch how they treat other people — not just how they treat you. Personality is defined as our stable way of thinking, feeling, and behaving across time and context. If someone is charming and attentive to you on a first date, but they are dismissive and rude to the waiter or the Uber driver — pay attention to that. How they treat people who can’t do anything for them is often more revealing than how they treat you when they want something from you. If you see a consistent pattern of cold, callous manipulation or cruelty toward others, and you’re telling yourself that’s never going to come your direction — you might be mistaken.
It’s also worth leaning on your wider social network. Research by Nick Epley and colleagues at the University of Chicago shows that while individuals are generally poor at detecting deception in isolation, group accuracy significantly improves when people are allowed to discuss their impressions together before reaching a collective judgement. The same principle applies to personality assessment. If you have friends or social connections in common with a new partner or colleague, their impressions matter. Reputation exists for a reason.
Q: Once we are entangled — in a toxic job or a destructive relationship — how do we get out without being destroyed in the process?
The advice has to be genuinely practical here. Especially in domestic situations where there has been violence in the past, the hard truth is that you simply cannot leave those relationships in the same way you might leave another. Leaving can be physically dangerous — the period of separation is often the time of highest risk. In those situations: reach out to domestic violence organisations or a trusted person in your life. Make a plan. Leave when they’re not around. Change your routines. And wherever possible, shift subsequent interactions to text rather than in person.
That last point is one of the most practically useful pieces of advice I can offer, and the research supports it. People with these dark personalities tend to have real power of persuasion and dominance in person — an in-room presence that can make you feel like you’re losing your grip on your own reasoning, second-guessing decisions you’d already made clearly. That power gets significantly diminished when they are reduced to words on a page. Text removes their ability to use physical presence, tone, and proximity against you. It also creates a written record — which matters if things escalate further.
In work situations, the harder thing is often not the actual leaving but making the decision to leave — because of what psychologists call the sunk cost fallacy. You’ve invested years in this job, you’ve built something here, and leaving feels like letting all of that go to waste. But past investment is not a good reason to continue accepting future harm.
One interesting way to break through that sunk cost thinking is to shift the frame entirely: rather than thinking only about the cost of leaving to yourself, think about the cost of staying to the people around you. If you come home every day short-tempered with your children, or unable to be present because the stress of this job is so overwhelming — you might be willing to absorb the abuse from a bad boss yourself, because you have talked yourself into believing you can handle it. But are you willing to put your family through the downstream effects of your staying? Sometimes thinking about the cost to the people you love most is the thing that finally tips the decision.