Though it would be more interesting to most to pick something obscure, I have to go with Cogito Ergo Sum. I think there is a deeper meaning behind “I think therefore I am” than most people realize. It is not simply an affirmation of personal existence. It is, more importantly, the enunciation of the only thing, within the confines of Western logic, that is actually, empirically provable. All else is extrapolation built upon scaffolds of ever increasing complexity.