Full Idea
A proof of the principle of sufficient reason has often been sought, but always in vain.
Gist of Idea
Proof of the principle of sufficient reason cannot be found
Source
Immanuel Kant (Critique of Pure Reason [1781], B265/A217)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.321
A Reaction
This might, of course, be because the principle is false. However it is quite a good candidate for an a priori, or even innate, principle of thought in rational beings. Gödel's Theorem suggests why the enterprise of proof would be doomed.