We only speak of faith when the one who believes does not know why he believes. But even so, for the believer himself the thing he believes in is perfectly clear and obvious to him — as if he saw it with his own eyes. This is because his faith is so strong (LM 62: 5).
Rebbe Nachman of Breslov; Rabbi Nathan of Breslov. Advice – Likutey Etzot (p. 30). Breslov Research Institute. Kindle Edition.