[throwaway81523]

Ideas are a dime a dozen in the sense that the same idea will often occur to dozens of people, on a dime's worth of effort. Relativity theory wasn't anything like that. Einstein made predictions that no one else was making. When one of them from GR was confirmed a few years ago, Lenny Susskind famously marveled at the foresight, saying "they didn't call him Einstein for nothing!".

[kelipso]

Problem then goes to how do I decide whether this particular idea is a dime a dozen or a unique idea... Everyone ends up going by feels when answering this question for any particular problem.