The course of human history would be a lot different if the simple idea "Look for reasons why you are wrong, not reasons why you are right" could spread earlier and farther. Experimentation has occurred for the whole of human history, but I think that little tidbit is what was missing, distilled down to a single sentence, but one from which everything else can pretty much be derived once you accept it.

Come to think of it, the course of the human present would be pretty different too.