Many riddles get many answers, some of them are correct, while some are wrong. Which one to accept has been discussed earlier, but I can't find a place where the "when" is discussed.
The reason why I ask is that I believe questions with accepted answers might be of less interest for other people. Also, I guess people look through other persons answers before posting an answer themselves. In my opinion, it's interesting to see the reasoning used when answering the question, both for correct answers, and for wrong ones.
Therefore, I would think that by not accepting the first correct answer the moment it is posted, people are encouraged to post interesting answers, both correct and incorrect ones.
Is there a consensus, and if so: what is it?