you will find that even demented people like ISIS fundamentalists understand gravity.
The raw nerve part is more to do with (or is) the above sort of comment.
I'm not directing that at you personally as I myself at times are guilty of this sort of thing.
If we go back to our young days, say school years, kids, the attitude or thoughts of many, or they simply don't think but assume what might be basic understandings to them, is not necessarily common across the board.
So a kid will comment or enquirer about something, only to receive ridicule or made fun of, the likes of, what a stupid question or the likes. Hence they drop it and just go with the flow and accept something as though it was so, but clearly don't now if this or that is fact = Gravity for example.
