Comments tell me why if I happen to be asking the question the comment is answering. You can't answer every "why" question in a comment. If you take "good code is self documenting" as dogma and say, "therefore I won't write comments", then probably you deserve what you get in the end ;-) But good code reduces the number of questions I might try to ask. That way I can get down to one "why" or possibly even no "why"s.

For example, I can write "a - 1" or I can write "-1 + a". If I write the second form people are going to wonder why I did it that way. Is there some reason why "a - 1" wouldn't work? Perhaps I don't have a - operator for a for some reason. But if I have no reason to write it the second way, then I should avoid doing it because then I don't have to write a comment saying, "I did it this way for no reason".

That's a simple and contrived example, but it holds true for larger code as well. There are ways of doing things that follow the programming culture most of us share. We shouldn't comment everything we do -- only the things that are unusual. Otherwise we'll be lost in comments. I'd rather read code to understand what's going on than English if I can help it.

So, the lack of need to write comments can indicate a good code base. However, like many things, it's a poor metric. The lack of comments does not indicate a good code base ;-) Similarly, some things are just complex, or unusual even when you have simplified it as much as humanly possible. Generally speaking, though, if you have a choice between code that needs a comment and code that doesn't need a comment, choose the latter.

Totally agree. It is impossible to show why one tradeoff was chosen over another without comments. Is there a loop unrolled for performance reasons? Is there a design goal that looks complex on the inside, but yields a simple, easy to understand API on the outside? I feel like "good code is self documenting" is a pitfall that devs always fall into believing on their journey to becoming a "Senior", and then somewhere along the way run into their old "good" code and can understand what it does perfectly well enough, but cant recall the circumstances that led them to arrive at the choices they made in writing that code.