From 30,000 feet, Britain’s coastline has a familiar sweep and shape. Zoom closer in – to, say, the cliffs of Dover – and it becomes less easy to comprehend. All you can see is a confusing series of jagged edges; down on the beach, peering at rocks with a magnifying glass, the coastline refuses to resolve itself into a regular pattern. The closer you look, the more that comprehension eludes you.

Reality is annoying like that: at every level of examination, it raises more questions than answers. There are always details that don’t fit, exceptions to rules, consequences that can’t be predicted. That’s why humans, who famously cannot bear too much reality, have evolved a method of coping with all this complexity: we lie to ourselves about how much we understand.

In 2002, the psychologists Frank Keil and Leonid Rozenblit asked people to rate their own understanding of how zips work. The respondents answered very confidently – after all, they used zips all the time. But when asked to explain how a zip works, they failed dismally. Similar results have been obtained with respect to flush toilets, piano keys, helicopters and bicycles. It doesn’t just apply to physical objects: people have been found to overestimate their understanding of climate change, the tax system and foreign policy.

We know a lot less than we think we do about the world around us. Cognitive scientists call this “the illusion of explanatory depth”, and sometimes just “the knowledge illusion”. Collectively, we know an awful lot, but each individual’s knowledge of the world is much sketchier and more superficial than he or she imagines. Only when pushed to explain what we think we know in detail do we briefly apprehend the epistemological abyss gaping beneath our beliefs.

I think this tells us something about what’s gone wrong with our politics. A consistent feature of those experiments is that after trying and failing to explain something, people accept that they don’t understand it as well as they thought they did. Humility sets in. But in our current political culture, that doesn’t happen. Among our political leaders it is almost unheard of to concede ignorance or even to accept that reality is complicated. They have no idea how zippers work, but they have very strong views on how to make them.

The disease of politics today is not populism, so much, as simplism: the oversimplification of complex problems. Politicians have always distilled intricate issues into soundbites and slogans – that’s part of the job. But Brexit has revealed something new: a refusal even to accept that there is a more complex reality behind the slogans.

Brexit is by far the most complicated, technical, multilayered policy problem this country has encountered. If you are not either bewildered or seized by apathy whenever any aspect of it is discussed in detail, you’re either misunderstanding what’s being said or you’re a member of a think tank. But most of the Tory leadership contenders, including and especially the one most likely to win, have made seemingly no effort before or since the referendum to advance their meagre knowledge of how the EU works, of the Irish border question, of international trade. They don’t even seem interested. Details are dismissed as unimportant, expertise as irrelevant. People who complicate things – which might be a good definition of an expert – are viewed with suspicion. Even as they fail and fail again, the politicians chant incantations to keep complexity at bay: Leave means Leave, no deal is better than a bad deal, believe in Britain. The slogans are eating us alive.

It is not a coincidence that politicians have developed this ardently simplist sensibility at a time when complexity is growing. Voters are simplists too. We live in an increasingly globalised, diverse, interdependent, technology-led society, but most of us don’t like to think about it. We take for granted enormously complex achievements, such as the presence of milk in your supermarket, or the phone in your pocket.

Similarly, the number of voters who truly understand the immigration system, or how schools are funded, is tiny (it’s almost an axiom: any issue worthy of public debate is too complicated for most voters to understand). But that doesn’t stop us from having strong opinions on them. Simplist solutions are seized upon because we don’t like to feel that we don’t understand things. When you don’t understand something, you feel less sense of agency over it, and as the 2016 Leave campaign realised, people get scared and angry when they don’t feel in control.

Simplism is changing the way we feel about each other, too. Dan Kahan, a Yale professor, is one of America’s leading experts on political polarisation, and one of his findings is that partisanship results from incuriosity. If you have a very different opinion to me on immigration, that might be because you have a very different experience of it from me. But to contemplate your different life experience requires an expense of brainpower to which most of us are unwilling to commit. It’s more efficient to dismiss others as bigoted or gullible.

Simplisms vary. The right likes to explain as much as possible with reference to the perfidy of foreigners. The left’s preferred strain of simplism is conspiracy: every social ill can be explained by the existence of a self-serving elite. Liberals assume everyone else is less intelligent.

A zip, by the way, consists of two tracks with dozens of teeth, each of which has a hook and a hollow; the trick is to latch every hook one on side into a hollow on the other. For that to happen, each tooth must be exactly the same size and shape and perfectly positioned on the track. Everything depends on everything else. Details matter. It’s a pity nobody in politics believes in them. Simplism is driving us into the sea.