The best part is when the duplicate is related to your question, but the duplicate question is structured differently so you don't know how to apply its answers to your question. Sure, if you already knew the answer the duplicate answers make sense, but without that knowledge (hence why you asked in the first place) they are completely unhelpful.
If the duplicate doesn't answer your question, you're supposed to edit your own question to indicate why the linked question wasn't helpful. At that point you're supposed to magically attract enough attention to get the question reopened. Unfortunately it rarely works out that way.