Full Idea
I make mistakes because the faculty of judging the truth, which I got from God, is not, in my case, infinite.
Gist of Idea
Error arises because my faculty for judging truth is not infinite
Source
René Descartes (Meditations [1641], §4.54)
Book Reference
Descartes,René: 'Discourse on Method/The Meditations', ed/tr. Sutcliffe,F.E. [Penguin 1968], p.134