Stress knows who it’s talking to
A lab in Freiburg put 121 people through a deliberately uncomfortable half hour, then watched how they treated two different people afterwards. The same stress produced two opposite responses. Which one you got depended entirely on who you were to them.
There are two stories about what pressure does to people, and they contradict each other.
The first one everybody knows: fight or flight. Under threat you pull in, guard what’s yours, get sharp. The second is quieter and newer: tend and befriend. Under threat you reach for people, seek company, soften.
Both have evidence behind them. Which has been an awkward problem for a long time, because they can’t both be the whole answer. Study after study kept landing on one or the other, and the field kept assuming somebody’s method must be off.
A paper published this week suggests nobody’s method was off. The question was.
What they did
Laura Oswald and colleagues at the University of Freiburg wondered whether the missing variable was simply who is standing in front of you.
They recruited 121 healthy young adults — 62 women, average age just under 24 — and put them through the Trier Social Stress Test for Groups, which is about as unpleasant as psychology gets while remaining entirely above board. Five minutes to prepare. Then a twelve-minute speech, then eight minutes of mental arithmetic, delivered in front of a jury in white coats who offered no encouraging feedback of any kind. Not hostility. Just nothing.
Saliva samples, heart-rate recordings and people’s own ratings confirmed it worked. Cortisol went up, heart rates went up, and participants said, unsurprisingly, that they felt stressed.
Then came the interesting part. Each person made a series of decisions involving real money across four established games — measuring trust, trustworthiness, sharing and willingness to punish. They made those decisions twice over. Once involving another participant who hadn’t been through the stress test at all. And once involving a member of the jury who had just helped put them through it.
Same person. Same stress. Two audiences.
What they found
The split was clean.
Toward the peer, people made an average of 2.52 trusting choices; toward the jury member, 2.02. Trustworthy choices: 3.06 versus 2.40. Sharing: 2.83 versus 2.27. And punishment ran the other way — 0.74 toward the jury member against 0.54 toward the peer. Every one of those gaps was statistically significant.
So: tend-and-befriend toward the stranger who might yet be an ally. Fight-or-flight toward the source of the pressure. Not two competing theories. One response with a sorting mechanism built into it.
Two further details are worth holding onto. The pattern didn’t differ meaningfully between men and women. And — this is the one that surprised us — how much someone’s cortisol or heart rate had spiked didn’t reliably predict how differently they treated the two people. The sorting wasn’t a function of how hard you were hit. It was a function of who was in front of you.
As the researchers put it: “individuals adapt their behavior toward others depending on the social role of their interaction partner.”
The limitations are real and the authors say so plainly. Everyone in the study was stressed — there was no calm comparison group — so it isn’t possible to tell whether stress raised cooperation with peers, lowered it toward jury members, or did both at once. The peer decisions always came before the jury decisions, which leaves room for order effects. The participants were young, healthy and few. The stressor was artificial, the evaluators deliberately cold, and the interactions took the form of money games rather than anything resembling a Tuesday. Studies with a non-stressed control group, friendlier evaluators and more natural encounters are the obvious next step.
What we keep thinking about
This is a laboratory finding about strangers and small sums of money. It is not a finding about your marriage, your team, or the person you were short with on Thursday, and we’d rather not pretend otherwise.
But the shape of it stayed with us.
Because the way most of us narrate a hard week is global. I was a mess. I was horrible to everyone. I fell apart. It arrives as a single verdict covering all of it, and once it’s arrived, it’s very difficult to argue with.
What this study describes is not one blunt reaction at all. It’s a response that discriminates — that leans toward some people and guards against others, and does so according to a logic that isn’t random even when it isn’t chosen. If something like that runs in ordinary life too, then “I was a mess” is not so much harsh as imprecise. It flattens a pattern into a judgement, and you can’t do anything with a judgement.
Which is not a licence, and we want to be careful here. Understanding why you pulled away from someone is not the same as it being fine that you did, and nothing in a lab study excuses anything. But you can only make a repair you can locate.
That’s roughly the thinking behind a small design decision of ours. Nagi’s check-in is four taps — mood, sleep, energy — just noted, as the days go by. It doesn’t score you, rank you, or tell you what any of it means; it isn’t a clinician and it doesn’t diagnose anything. It holds the record privately: no name, no email, an anonymous ID rather than a name. Part of why we built it that way is that a week looks different laid out than it does remembered, and memory has a habit of rounding everything down to one word.
The bit we’d underline
You probably weren’t uniformly anything.
Under pressure, something in us is still sorting — still deciding, somewhere below the level of choosing, who to move toward and who to protect ourselves from. That’s worth noticing before you sentence the whole week.
If you want a private place to start noticing your own patterns, Nagi is on Google Play and the App Store — or in your browser at app.nagiandme.app. The first 15 messages are free. No name, no email. Just you, checking in.
— The Nagi team
Source: A new study explains why stress makes us both cooperative and defensive, PsyPost, 3 September 2026, by Bianca Setionago. Underlying study: Oswald, L., Dvorak, F., Jamieson, J. P., Heinrichs, M., & Schiller, B., “Tend-and-befriend toward peers, fight-or-flight toward stressors: A dual response to stress”, Psychoneuroendocrinology. Design: laboratory study, 121 healthy young adults (62 women, mean age 23.64), all of whom completed the Trier Social Stress Test for Groups (five minutes’ preparation, a twelve-minute speech and an eight-minute mental-arithmetic task before a non-encouraging jury), with cortisol, heart rate and subjective ratings confirming a stress response; participants then made incentivised decisions in four economic games measuring trust, trustworthiness, sharing and punishment, once involving an unstressed peer and once involving a jury member. Stated limitations: every participant underwent the stressor, so with no non-stress control group the study cannot establish whether stress raised cooperation toward peers, lowered it toward jury members, or both; peer decisions always preceded jury decisions, leaving possible order and comparison effects; the authors call for studies with a control group, friendlier evaluators and more naturalistic interactions.
Nagi is a mental health companion, not a medical device, and nothing here is medical advice. If you’re struggling, please reach out to a professional or someone you trust.