I have found Stack Overflow to be very useful in finding answers to my technical questions. (Reminds me of how the Internet used to be pre-commercialization). I value its ethos and have found most answers to be on point.
However, I recently answered a question (How do you stop the XCode debugger from autocompleting without options?) with what I though was a helpful (== "useful") answer and was surprised when the original poster marked it as "not useful". I don't really care about losing the single reputation point, but I am concerned that this will make me think twice about posting answers - something I feel is counter-productive to Stack Overflow.
So, I would appreciate some comments on how experienced Stack Overflow users decide when they consider an answer to be "not useful".
Thanks in advance.