If you mean faith in a religious sense, then personally it has no meaning at all.
One of the reasons I like Yoshinkan is that when I was first looking to start training, it was the only dojo I found that didn't spend half the class doing ki exercises or sitting around while Sensei read bits of books to people & discussed it.
I was there to train, not sit around & talk about training... lol
As for faith in the techniques themselves, I think you have to have faith in them. When you doubt your technique, you start to tense up & do unconsciously doing little things that cause your technique to fall to bits totally. It seems like a bit of a self-fulfilling prophecy.