Cunningham's Law states: "The best way to get the right answer on the Internet is not to ask a question; it's to post the wrong answer."
When asking a question, the user is hoping someone will take time out of their day to charitably assist them. When posting an answer, users who disagree with the answer often feel compelled to correct it, thus producing the correct answer for the original poster.
An early XKCD comic illustrates this:
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