I remember my physics teacher explained this one day. He said: We start with a poor but general understanding, that things fall toward the ground. This is like

I remember my physics teacher explained this one day. He said: We start with a poor but general understanding, that things fall toward the ground. This is like a big square of stone, it's familiar but undefined and for most purposes it's useless. We advance our understanding, chipping away at the stone to reveal a model that is more practical. To an understanding that is beyond simply observations. Objects fall at 9.81m/s/s. You'v now got an octagonal disc of stone, you could run a cart on it, but you probably wouldn't get far before you break your tail bone. Then we go beyond just passively observing and begin testing. We find data, compile it and test it against models. This is like using a finishing chisel and sand paper. You get the Theory of Relativity, it's smooth, it's polished and it's a perfect wheel. Now just wait for someone to invent a hover car and your wheel and the theory of relativity are old news.