Full Idea
What we believe the most, everything a priori, is not for that reason more certain, just because it is so strongly believed. Rather, it is perhaps a consequence of the condition for the existence of our species.
Gist of Idea
Strongly believed a priori is not certain; it may just be a feature of our existence
Source
Friedrich Nietzsche (Unpublished Notebooks 1884-85 [1884], 25[307])
Book Reference
Nietzsche,Friedrich: 'Fragments from 1884-85 (v 15)', ed/tr. Loeb,P.S./Tinsley,D.F. [Stanford 2022], p.78
A Reaction
This is in defiance of Leibniz and Kant. His proposed explanation is not very convincing. Russell agreed with Nietzsche.