Principle of Sufficient Reason

Nothing happens without a reason why it is so rather than otherwise.

Alongside the principle of contradiction, one of Leibniz's two pillars of all reasoning. Every fact has an explanation, even if we cannot discover it. The principle drives some of the strongest arguments for God (the cosmological argument: what is the sufficient reason for the universe?) and some of the deepest critiques of metaphysics (Schopenhauer wrote his doctoral dissertation on its limits).