Two passages that say that you already know the truth (once it has been revealed to you), but you have to search for it anyway:
Thomas Aquinas, On Boethius on the Trinity, part 1, question 2, article 3, translated by Rose E. Brennan: "If, however, anything is found in the teachings of the philosophers contrary to faith, this error does not properly belong to philosophy, but is due to an abuse of philosophy owing to the insufficiency of reason. Therefore also it is possible from the principles of philosophy to refute an error of this kind, either by showing it to be altogether impossible, or not to be necessary."
Eliezer Yudkowski, Rationality, chapter 188:
"But perhaps it is not quite as exciting to see something that doesn’t look Bayesian on the surface, revealed as Bayes wearing a clever disguise, if: (a) you don’t unravel the mystery yourself, but read about someone else doing it (Newton had more fun than most students taking calculus), and (b) you don’t realize that searching for the hidden Bayes-structure is this huge, difficult, omnipresent quest, like searching for the Holy Grail.
It’s a different quest for each facet of cognition, but the Grail always turns out to be the same. It has to be the right Grail, though—and the entire Grail, without any parts missing—and so each time you have to go on the quest looking for a full answer whatever form it may take, rather than trying to artificially construct vaguely hand-waving Grailish arguments. Then you always find the same Holy Grail at the end."