There are a couple of ones that are obvious now but blew me away when I was a little kid. For example:
-rockets thrust doesn't need ground to push off of
-the earth isn't any farther from the sun during winter
There is also that realization at some point in a person's life where you figure out that "history" (at least what you learn in elementry or high school) is as much propoganda as fact. The winner always writes the hisotry books and far too often people seem to take their accounts at face value. Even in recent hitsory, I rember when I first heard that the USSR killed way more Nazis than the USA did I though it was total BS, but looking at WWII the eastern from is FAR more important than the western front and yet all you hear growing up in America are D-Day and on (which occured after the war was more or less already decided).