A comment should be worth it's maintenance weight.
What I mean by that, is that as code gets refactored, comments often get stale and incorrect (which leads to bugs later on because programmers still thrust them).

Unlike what they teach at school "the more comments, the better", many developers (especially those of the clean code methodology), now believe that:
- Code should be readable and easily understandable without comments
- If the code is not easily readable and easily understandable, it should be refactored so it is.
- If it's not possible to refactor it, then comments need to be added to make it understandable. But this is a sign of weakness, because comments come at a maintenance weight.
- Of course, code that is not understandable and not commented is still the worst kind of code.