He who knows others is wise. He who knows himself is enlightened.

Reading other people is a skill you can practise from a safe distance, and it flatters you while you do it. Turning the same attention inward removes the safety, because there is nobody to be right about except yourself and nothing you notice can be filed away as someone else’s problem. That is why self-knowledge is rarer than shrewdness about others, not because it is harder but because it is more expensive.

Next time you find yourself neatly diagnosing somebody, pause and ask whether the same description fits you in a slightly different costume. The answer does not have to be shared with anyone.