I WAS IN MY early 20s when I discovered just how much ‘truth’ differs from person to person. I was a journalist on a local daily newspaper. I found it interesting that witnesses to an incident – a fatal fire, a car crash, an industrial dispute – had different views of what they had seen. Incredibly different views, sometimes. Almost as if they had been at different incidents.

Some things are unequivocally true, of course. Today’s temperature can be measured. The number of years I have spent with the woman I love can be measured.

Quite a lot of the other stuff, it seems to me, is open to interpretation. So much so, that I used to say – rather cleverly, I thought, that – “truth is relative to where you happen to be standing”. And so I became what philosophy calls “a relativist”, although I wasn’t educated enough to know that at the time.

Later, and as a result of spending many hours in interviews of one sort or another, I began to look at the psychology of truth. And I got even more interested.

Everybody, every individual, is different. Nobody has ever had anyone else’s brain. And so everybody – every last one of us – is unique. But don’t get cocky: as individuals, we are all just a mix of our experience, our skills, our values and our genetics.

So, somebody who was bitten by a dog when she was little will always see a barking dog as a threat, where somebody who wasn’t may see a playful and excited puppy.

In this way, we filter our experience of the outside world, and there is a strong argument that we don’t really see the world as it is at all. We create our own version of it.

Memories are especially difficult. Every memory you have is changed by the process of recall. Your mood is different as you bring the memory to mind, the place is different, the people you are with are different: the memory becomes different. The very language you use to describe it makes it different.

So, what does this mean for our sense of being in the world, our personal existence?

I have written elsewhere on this site about ‘cognitive bias’ and the idea that people make intuitive decisions then search for the data to support those decisions, ignoring any that do not support their hypotheses. It’s a fashionable theory and has been the subject of many recent studies.

What does one do then, in the case of – for instance – a general election? The answer, of course, is that one chooses the narrative one prefers: the one that fits most precisely with one’s values and experience. And, actually, everybody is cool with that, if you think about it.

And what does one do, in the case of – for instance – the collapse of a friend’s marriage? The answer is the same. One chooses the story one prefers: the one that fits most precisely with one’s experience, knowledge and values. It’s the closest thing we have to certainty.

Is the answer true? Yes, entirely. For you. And, frankly, nothing else matters. There is no other measure. You can only see the world through your own eyes.

Truth can be elusive because we can’t get at all of the empirical data. In the end, you just have to go with what you’ve got. And that’s what we all do.