A long time ago, as I first failed to wrap my head around quantum mechanics, I was reassured by Richard Feynman and Leonard Susskind, who gave me an excuse. Our brains didn't evolve to understand the quantum world, they said. The long, sunny, tough childhood of Homo sapiens took place on the African savannah. Our minds evolved to find fruit, to recognise each other, to hide from leopards, and to throw spears. So it's not surprising that we find it difficult to reason about how an electron doesn't exist in one place but is spread out around its parent atom like peanut butter on bread, or about how the faster you move, the slower you age compared to a stationary friend. These effects are undoubtedly true: transistors wouldn't work without the first, and GPS wouldn't function without the second. But they are damn hard to understand.

This was my first introduction to the relativity of thought: the idea that there are many ways of thinking about the world around us, and I just happen to be using one of them. The next big one was the Sapir-Whorf hypothesis (which due to its vagueness is more an approach than a hypothesis), the idea that our language shapes our world view. This is the big brother of the old saw that the Irish can't say no because they don't have a word for it, or that for the same reason the Filipinos can't say sorry. It's the idea that our world-view is formed by our language and that some thoughts can only be had in a particular language.

These insights were very powerful and, armed with them, I felt much better equipped to understand the world. I fancied they liberated me from arbitrary concerns, much as a lapsed Christian no longer has to worry about the doctrine of the Trinity. And I felt that others, especially politicians, could benefit greatly from asking themselves whether the words they were using actually meant something.

There have been many more insights since. Psychological disorders, such as psychopathy and borderline personality disorder, are more arbitrary constructs than concepts which emerge naturally from the world; every edition of the Diagnostic and Statistical Manual of Mental Disorders adds and removes conditions from the list. The relativity of thought confers freedom from definitions: whereas I used to struggle to write down the real meaning of ideas like leadership and consciousness, I am now at peace with the possibility that they could each just be instantiated in all of us, woven together from our memories of leaders or conscious beings - just like our individual definitions of really tasty food. Do fish feel pain? The answer depends on your definition of pain, though luckily we agree more on what a fish is.

The relativity of thought has become ever more troublesome since the Internet turned the slow-moving currents of political thought into a roiling Charybdis of conflict. Political concepts have always been fluid - what makes a liberal? New concepts are being created at a fantastic rate.

But the relativity of thought can also be dangerous, because it makes it much easier to accept the points of view of others. Some of the hardest friendships and relationships are those in which two people don't share a common language. Some of the most damaging conflicts are those in which two people are fighting over universal truths, as in gaslighting, where the assailant convinces the victim that their perceptions and memories are actually wrong.

One of the strongest and most convincing psychological illusions is the idea that we will be much the same in ten years. It's convincingly disproved by asking people to look back at how they were ten years ago - in nearly all cases, very different. We change as we go through life. People flip between ends of the political spectrum, and sometimes flop back. One of the biggest dichotomies is that between opportunity and responsibility, between potential and merit. Should we try and fail all our students, so that only the best qualify - or should we try and support all our students, so that they all end up better? Should we support the weak, so that they can grow into the strong - or should we prioritise the strong, so that we can stamp out the weak?

The more you accept the relativity of thought, the more you are likely to change position. So I've come to accept, as time passed, that although the main insight a child can have is that there are other ways of thinking about the world, one of the most important realisations an adult can have is that although there are many ways of thinking about the world, you have to pick one and cleave to it. Even though there are two sides to every question and you can always see the opposing point of view, flipping between the two is worse than taking the wrong point of view, for it means you abdicate your identity.