By Karl Popper
It is impossible to avoid all mistakes, or even all those mistakes that are, in themselves, avoidable. Mistakes are continually being made by all scientists. The old idea that mistakes can be avoided and that one is therefore in duty bound to avoid them must be revised: it is itself a mistake.
It still remains our duty to do everything m can to avoid mistakes, but it is precisely in order to avoid them that we must be aware of the difficulty in avoiding them, and of the fact that nobody succeeds in avoiding them all; not even the most creative scientists who are guided by intuition succeed. Although we can do nothing without it, intuition is more often wrong than right.
We must, therefore, be constantly on the lookout for mistakes, especially our own mistakes. When we find them we must remember them; and we must scrutinize them from all aspects, in order to understand better what went wrong.
A self-critical attitude, frankness, and openness towards oneself become, therefore, part of everyone’s duty.
Since we must learn from our mistakes, we must also learn to accept, indeed accept with thanks, their being pointed out to us by others. When we draw other people’s attention to their mistakes, we should always remember that we ourselves have made similar mistakes. And we should remember that the greatest scientists have made great mistakes. This is certainly not meant to imply that our mistakes are generally forgivable: we must never let our attention slacken. But it is humanly impossible to avoid making mistakes, and when we draw the attention of others to their mistakes, we might help them by pointing this out too.
We must be clear in our minds that we need other people to discover and correct some of our mistakes (as they need us). Especially people who have grown up with different ideas, in a different cultural atmosphere. This too leads to toleration.
We must learn that self-criticism is the best criticism; but that criticism by others is a necessity. It is nearly as good as self-criticism. Rational (or objective) criticism must always be specific: it must give specific reasons why specific statements, specific hypotheses appear to be false, or specific arguments invalid. It must be guided by the idea of getting nearer to objective truth. In this sense it must be impersonal, but also sympathetic.