‘Lessons must be learnt’. So everyone intones each time there is a report or a review or an inquiry into something that has gone wrong. And, of course, that is always right. Lessons must be learnt. But from my experience there are two main reasons why lessons are not always learnt.

First, we think that the lesson we must learn is that when something like this – whatever the review or inquiry was about – occurs again, we will be ready for it. We shall have ensured that everyone understands what went wrong and there will be training so that they realise what they must do to stop this happening again. Yes, we must do this, though most of the time we only have to have what went wrong revealed to know what we must do to stop it happening again.

But the reality is that things rarely repeat themselves in the self same way. The real lesson to be learnt is that we must be more alert to new ways in which mistakes can be made. Mechanical reflexes are no good when what is needed is for people to be more aware and thoughtful about what is happening around them and what they are doing, to look around, to stand back. Thoughtfulness and greater awareness is the lesson to be learnt.

And second, the reason we resist learning lessons is when we never quite believe what we are told. I recently spoke to some councillors concerned about violence. There had been a lot of police activity in their area but few concrete results. I told them about some evidence-based policing which is being trialled in parts of South Yorkshire where there are violence hot spots, which one of our superintendents told the VR executive board about recently. This has already been tried, tested and evaluated elsewhere – it is evidence-based.

Briefly, what the police do in those areas is to patrol very visibly for fifteen to twenty minutes a couple of times a day between the hours of 12 noon and midnight. They speak to anyone they meet, they tackle any crime or anti-social behaviour that presents itself, and so on. Above all, they draw attention to themselves and to the fact that they are in the area.

It seems that the word quickly goes round that the police are about. It has the effect of suppressing violence and other crime. And it has this effect over a wider area than the streets patrolled. It does not lead to crime, ASB or violence being displaced.

It only needs these short, intensive fifteen to twenty minutes of patrolling. Extending the patrols over a wider area or for a longer time brings no further benefits. All of which is counter-intuitive and so hard to believe. But this is the evidence-based lesson to be learnt.

Would the councillors learn it? No, they would not! They disbelieved the evidence. They simply would not accept that fifteen to twenty minutes was the optimum time. They knew better. This was one lesson that could not be learnt.