[kmoser]

Generalizations like that are theoretical, and don't always align with reality. There's nothing wrong with comments summarizing the "what", and in fact doing so is a good thing because it can describe anything from the intention of the code to the business logic. "This function merges array X with array Y, converting all the keys to lowercase because they will be used later by foo()."

The "why" can go out of date, e.g. "do X before Y because [specific thing in Y] is dependent on [specific thing in X]". If you rewrite Y to no longer be dependent on X, the comment is now out of date.

The reality is that any comment can go out of date at any time if the code it describes changes enough. But that's really no excuse for failure to maintain comments. Sure, in reality code is messy and inconsistently written, not even counting comments. Comments are an essential parts of your codebase, and while they are used exclusively by humans, that doesn't mean they are any less worthy of being updated and cultivated.