Musings on copyright and citing

Recently, one of my fellow grad students delivered a conference paper. Only afterwards, did he find out that someone had delivered almost the same paper at approximately the same time at another conference. So, who's work is it? Who should have cited whom???

Alternately, having been presented with various facts, I have come to my own conclusions. However, someone born 50 years earlier had seen very similar facts and come to the same conclusion as well. Due to this guy being born 50 years earlier, he was able to write it down first. Are my conclusions any less mine? Shouldn't I be able to claim credit for my own independent thoughts, even if someone else had a parallel thought process at some previous point in time?

Citing someone for an idea suggests that he or she is the only person to have ever come up with that idea, when really, he or she is just the earliest person to have written it down somewhere where the writer of a subsequent paper can find it.

Of course, there are also many published authors who will never get credit for what they've written, because their articles are buried somewhere in some library or lost in fire and will never be read again, so then the next guy can just put his name on the idea; until one of these lost copies is found, and then the next guy becomes a plagarist. Lovely.

So, refering back to another post, should I cite Hitler before stating "the current administration's policies are so outrageous that they can't be true...but what if they are?...no one would believe it!" because it is the same idea as Hitler expressed with "The great masses of people ... will more easily fall victims to a big lie than to a small one." He wrote it first. (Not to mention issues of "ideas" in translation!)