Many times I have answered questions only to be told to cite it. So I research and find somebody has already published it. With as much brains around here is it not possible to arrive at the same answer and not have to cite everything. I believe Einstein was a victim of this. When I draw a correct answer or even an answer that is a theory without proof do I have to cite it if I came up with the answer myself?
Without specific instance of where this occurred, I can only give general advice. This site is intended for professional physicists and students who are working towards that. We welcome non-professionals and non-physicists of course, but only when their questions and answers are up to the standards expected.
As such, most people here are academics or were trained in an academic setting. We therefore expect questions and answers to support the claims and conclusions made in them. This is done through citations of relevant information.
Now, we aren't as hardcore as a journal or conference. But for the most part, we expect answers to be supported by facts. These facts can include derivations and proofs if you did the work yourself and it is (mostly) original. And if the statement is so obvious that everybody in the field knows it to be true, then no citation is needed. For instance, nobody except a troll would demand a citation for $e=mc^2$. But if you came out and said "The equation you want is $e = mc^2 + 10$" -- well, you better be prepared to either cite where that comes from or provide all the details of how you derived it because that is not considered totally obvious to the experts.
So -- if you come up with an answer yourself, that's great, but you need to provide supporting facts if they are not immediately obvious. And if somebody is asking you to cite something, it means it is not immediately obvious.
This is true on this site, but more importantly it is true in all the work you do. It doesn't matter if it is an essay in high school or a journal paper that nets you a Nobel Prize. You must always cite claims and statements, or provide the derivations yourself.