THERE’S SOMETHING psychologists call “confirmation bias”. You can look it up on the internet if you like. There’s tons of stuff on it.

It’s a tendency for people to favour information that supports their preconceptions or hypotheses, without worrying too much about whether the information reveals or represents the truth.

We all do it, although some do it more than others.

It stems from an evolved tendency towards intuitive thinking: a tendency that gave us an evolutionary advantage on the plains of Africa, but is sometimes less useful in a 21st century urban setting.

In short, we make an intuitive decision and then – like a lawyer building a defence for her client – we go looking for evidence to support it. If we come across evidence that does not support our decision, we attack it or we dismiss it.

You can see examples of this in newspapers every day; it is commonplace.

When beliefs become personal values – the rules by which an individual chooses to live his life – confirmation bias can have an unfortunate effect. Any challenge to belief becomes a challenge to the value system and an attack on the individual’s sense of self. It has to be rejected, and angrily if that’s what it takes.

I came across a classic example of this recently. A likeable young man who had been publicly challenged on something he believed in – something rooted in his professional skill set – began to show visible signs of stress.

He was still stressed when I chatted to him over a drink later, and he said things that – objectively – would probably have sounded strange to him  in a calmer state of mind.

At one point in a perfectly normal conversation he said: “I don’t care what you say, I’m never going to change my mind…” (What? Never?)

Later, he said: “I don’t know anything about journalists or about journalism, but I get the impression that most journalists are up themselves.”

What I heard was: “I have no evidence on which to base an opinion, but my opinion is …”

I feared that it was, for him, a repeating pattern – and well on its way to becoming a fundamental part of the way in which he chooses to think.

I didn’t take offence (it’s a choice one has), and I guessed that further debate would have caused him more stress, so I gently changed the subject. Within minutes he had found something else to be aggrieved about.

My best guess was that the challenge to his identity – which was entirely in his own head – had triggered a limbic system response: the well-known “fight or flight” reaction. And he was up for a fight – any fight.

You may recognise some of these symptoms: this is a common enough scenario, and one that most of us will have experienced to a greater or lesser extent.

For an unfortunate few, however, confirmation bias has a tragic impact on their lives. Unable to accept the possibility that they are not “right”, they adopt an unhelpfully inflexible view of the world and become habitually belicose. It’s a stance that can cost them their livelihoods and their closest relationships and leave them feeling “right” in absolute isolation.

This is not to suggest that intuitive thinking is necessarily bad, or that beliefs and values tie us down (although they can do, especially when they are not regularly overhauled). It’s merely to observe that flexibility in thinking may be aided by a reluctance to accept opinion as fact and a willingness to challenge beliefs and values – especially one’s own.