Nietzsche suggested that one of the most fundamental questions is whether the world is genuinely susceptible to rational explanation. This question, unfortunately, is almost never asked; we take it on faith- after all, we need faith in something.

This is also expressed nicely by Fernando Pessoa in The Book of Disquiet.

“Reason is faith in what can be understood without faith, but it’s still a faith, since to understand presupposes that there’s something understandable.”