Proof is Always Good to Find
For years I've read how the best explanation of the origin of the Earth/Moon system is that early in the Earth's existence it was struck by another planet and the Moon was formed from part of the Earth and the other planet, which was named Theia. Now further analysis of rocks from the Moon provide proof of that theory. The people who originally developed the models of that idea of the origins of the Moon have got to be happy about this discovery. No matter how good the models explain something I would imagine the discovery of physical proof to back them up is very satisfying.