Comments can lie. Code can't.

How often have you need code like this?

// Returns true.
return false;

Whilst a comment like this could have been true when it was written, the code can change independently of the comment - making them out of sync and the comment no longer true.

As the comment is not evaluated or executed, there isn't a way to validate whether it's still correct, so whilst it could be, it may not be.

Comments should describe why the code is needed, not what it does.

If a comment describes the functionality, it can be refactored and extracted to a class, method or function - a.k.a. self-documenting code.

But, if you want something that will alert you if the functionality changes, look into automated testing.

If you have a passing test that suddenly starts to fail, you know the behaviour has changed.