Besides it is an error to believe that rigour is the enemy of simplicity. On the contrary we find it confirmed by numerous examples that the rigorous method is at the same time the simpler and the more easily comprehended. The very effort for rigor forces us to find out simpler methods of proof.
David HilbertWe do not master a scientific theory until we have shelled and completely prised free its mathematical kernel.
David HilbertMathematics is a game played according to certain simple rules with meaningless marks on paper.
David Hilbert