“Complain less” is one of the very best pieces of wisdom. That is positively correlated with criticizing other people less, though it is not identical either.

If you criticize X to Y, Y wonders whether you criticize him to others as well. This problem can increase to the extent your criticism is biting and on the mark.

Criticizing others is a way of building trust. In a three-way friendship with X, Y, and Z, if X establishes that he and Y can together criticize Z, that may boost trust between Y and X, and also increase X’s relative power in the group. Criticizing “Charles Manson” doesn’t do this — you’ve got to take some chances with your targets.