I had the podcast on in the background while I was doing something else entirely. I wasn’t really listening — it was noise, company, the usual ambient accompaniment to work that doesn’t require full concentration. And then one sentence landed differently and I stopped what I was doing.
The guest was Hannah Critchlow, a neuroscientist at Cambridge University and author of 21st Century Brain, speaking on the Live Well Be Well podcast with Sarah Ann Macklin. What she said wasn’t complicated. It was one of those things that sounds almost too simple until you realise it explains a pattern you’ve been living inside for weeks without quite naming it.
The pattern, in my case, was stress. A particular kind — not the acute, actionable kind, but the low-grade, constant kind that doesn’t point at anything specific. I’d been attributing it to workload, to season, to the ordinary accumulation of things. What Critchlow said in that moment made me think it was something more basic than any of those. It was the not knowing.
And that turns out to be a very precisely documented problem inside the brain.
The shock study that reframes everything
The clearest demonstration of what Critchlow is describing comes from a study run at University College London by Archy de Berker and colleagues. The study found that participants were most stressed not when a shock was guaranteed, but when the probability hovered around fifty per cent. A certain shock was, measurably, less distressing than an uncertain one.
The vast majority chose the shock.
Not because they were confused about pain. Not because they miscalculated the odds. But because ending the uncertainty felt more pressing than avoiding the discomfort. The not-knowing was, for most people, worse than the thing they were afraid of. The study, published in Nature Communications in 2016, found that uncertainty itself generates a stress response — and that the magnitude of that response tracks the degree of uncertainty, not the magnitude of the potential bad outcome.
Critchlow’s framing of this is what stuck with me. She describes the brain as fundamentally a prediction machine — a system that is constantly building models of what is likely to happen next, updating them against incoming information, and using the accuracy of those predictions to regulate everything from attention to cortisol levels. Uncertainty is not just unpleasant. It is, in a very literal neurological sense, a failure state. The brain cannot do its core job — predicting, preparing, regulating — when it doesn’t have enough information to build a model.
This is why chronic uncertainty produces what looks externally like anxiety but is, at the biological level, a system under persistent load. The brain keeps trying to resolve the open loop. It keeps returning to the unanswered question, running the same calculations, looking for the information that would let it close the file. And when that information doesn’t arrive — when the situation stays unresolved, the outcome stays unclear — the system keeps running. That hum you can feel but not locate is the brain doing its job in a context that makes the job impossible to complete.
I had to go and find the Sarah Ann Macklin writeup of the episode after I listened, because I needed the research to be real and not just a thing I’d half-heard.
It was real.
Most of what I had been calling stress for the past month was, almost certainly, this: an accumulation of unresolved open loops that the brain kept returning to because that is what it is built to do.
Not all brains respond the same way
Here is where it gets more interesting, and where the conversation moves from diagnosis to something more useful.
Critchlow describes what she calls the duck-rabbit brain — a reference to the classic perceptual illusion in which the same image can be read as either a duck or a rabbit depending on how you look at it. Some people can flip between the two interpretations easily. Others lock into one and struggle to switch. And this difference — in how fluidly someone can hold two competing interpretations simultaneously — turns out to be a proxy for something deeper.
The people who can flip quickly tend to have higher tolerance for ambiguity. Their brains don’t register uncertainty as a threat in the same way. They stay open, flexible, curious — which is exactly what the research on need for cognitive closure has been describing for decades. High need for closure — the urgent drive to reach a definitive answer and stop the discomfort of not knowing — predicts avoidance, rigidity, and poor performance in ambiguous situations. Low need for closure — the ability to sit inside uncertainty without the pressure to resolve it — predicts creativity, flexibility, and the capacity to hold complex problems open long enough to find non-obvious solutions.
The most creative people in any room are not, typically, the ones who reach conclusions fastest. They are the ones who can stay inside the question longer. The ones whose brains don’t treat an open loop as an emergency. What looks like comfort with ambiguity is, at the neural level, a less reactive stress response to prediction failure — a brain that can keep the model running without demanding an answer before one is available.
What this means for the rest of us
Critchlow is careful not to present this as a fixed trait — the brain you’re born with, take it or leave it. Neuroplasticity research consistently shows that the brain’s responses to uncertainty are trainable, to a degree, through deliberate exposure and practice. The mechanism is not unlike the one that governs physical stress responses: what the system experiences as threatening under novel conditions becomes manageable as familiarity builds. Tolerance for ambiguity is not a personality type. It is closer to a capacity — one that, like most capacities, can be developed.
But the prerequisite for developing it is understanding what is actually happening. Most people who experience chronic, diffuse stress do not think of it as uncertainty intolerance. They think of it as having a lot going on. The two are not mutually exclusive, but the former is much more tractable than the latter. You cannot reduce having a lot going on by thinking about it differently. You can, with practice, change how much cognitive load unresolved uncertainty imposes.
Critchlow’s other suggestion — and this one is nearly as simple as the one that stopped me mid-task — is about what the brain does when it is allowed to wander. When you walk without a destination, or sit without a task, or let your mind drift in the shower, your brain produces what are called alpha waves: slow, rhythmic electrical oscillations associated with calm, clear thinking. Research on the default mode network suggests this undirected wandering is not a waste of cognitive resources. It is where the brain consolidates, connects, and — not incidentally — closes some of its open loops in ways that directed thinking cannot.
The period of time you spend staring out of a window is not a detour from the work. It may be where some of the most important work actually happens.
The productivity of sitting still
What I took from the episode — and what the research it referenced confirmed — is that the brain’s relationship with not knowing is not a problem to be solved so much as a system to be understood. The discomfort is real. The drive to resolve uncertainty is real and deeply biological. But the people who are most effective inside ambiguous situations are not the ones who have overcome that drive — they are the ones who have, somehow, learned to recognise it for what it is without being fully governed by it.
That is a harder thing to teach than most productivity advice suggests. But it is a more honest account of what creative capacity actually involves: not the absence of discomfort with not knowing, but the ability to notice the discomfort and stay in the question anyway. The open loop, held with some degree of ease, is where the interesting work lives.
The shock, it turns out, is not always the right choice just because it closes the loop faster.
