I think the biggest reason is new members not knowing how things work around here will come on and ask a question of basic knowledge which may have been asked before. Many times unless it is word for word the system will not see it as a duplicate and it will show up on the board. Many slip by those that flag duplicates during times that activity is very low and it may take a while before it is found and merged with another question.

1) Many questions of general interest have already been asked. An exception are, of course, questions about present events. Also, many questions about the function of the site have been asked. 2) It seems that many people just ask their questions without caring about them being duplicates. But if you really want a quick answer to your question, you can often find it by looking at very similar questions. Except, of course, you are just asking questions to collect points... You have to realize that in the moment where you ask a question, and if you have not disabled that feature, Answerbag makes some propositions of similar question which have already been asked. 3) I just started the process of asking with the following question: "I wonder why there are so many duplicate questions!? I try to think of an original question and the next thing i know AB tells me its a duplicate! OMG i hope THIS question is not a duplicate!" I got various category results (among them, the "Duplicates" category) and various question results, among them, your question, but also: - "How many duplicate questions do you think are asked daily on AB? Estimates?" - "Have you ever noticed just how many duplicate questions there are on AB? I just checked for "Why is the sky blue" and came up with about 12 asking the same thing! Duplicate flags FTW!!!" (only on the first page of results) If we just concentrate on the idea of the question, you will admit yourself, I think, that there is no big difference between those two: - "Why are there so many duplicate questions!?" - "Have you ever noticed just how many duplicate questions there are on AB?" One is just wondering about the many duplicates, the other is asking for a reason.(In this sense, they are also no real duplicates, in my opinion; but some could also consider them as such). 4) In a second step, I started to ask the simplified question: "Why are there so many duplicate questions!?" Here again, I found interesting question results (other than your own question): - "Why are so many people asking duplicate questions?" - "What the hell is with all the duplicates lately?" - "How many duplicate questions has one received? I just received 2 today." - "How many duplicate questions would it take for you to get bored to tears on AB?" - "How many duplicate "what came first the chicken or the egg" questions do we have on AB?" - "I find I am moderating questions on AB a lot more lately, as there are many duplicates. Do your find this to be irritating behaviour?" What do you think now? 5) See also this answer: "So many more duplicates questions , If people would just go down the list provided for them before posting a Question ? They can see their Question has already been asked " http://www.answerbag.com/a_view/2042065

Do you mean besides why is the sky blue?

But I have.