I ascribe to the notion that 'comments are apologies' (to my future self).

If a piece of code is weird, or slow, or you'd say "yeah, it's kinda janky" when describing to somebody, I usually write a comment about it. Especially if I've changed it before; to document some case that didn't work, or I fixed, or whatever.

When you operate on this basis, superfluous comments just melt away, and you typically end up documenting 'why' only when it's really necessary.

Try it out in your own codebase for a month and see how it feels :)