Taking Lynn's comments on confidence further, a question of experience arises in respect to memorization. Perhaps the way forwards on this thread is to share our thinking on how to memorize.
For myself, I have a trained visual memory which although not eidetic is very, very good. I developed it when young using a card game often known as Pelmanism, dealing a shuffled pack of cards out face-down on a table and then looking for pairs. Complicating it somewhat involves colour-matching, both black 2s, for example.
My first read-through on a new piece is to do with what the line I'm singing's doing, musically. The second is how it relates to everything else that's happening. The third comes back to the line and is done slowly, the first time I'm trying the line out loud. It's a sketch, trying to find some anchor points in the piece. Then I work the sections resulting up in detail, deciding how to do it.
The next stage is closely related to what the dance world calls body memory. It means going over it time and time again, repeating it until I can do it in my sleep - sometimes literally, it seems. Having it on my mind when I go to sleep helps enormously, my mind integrates it far better.
Once I'm certain it conforms to the pro standard in "an amateur rehearses until he performs it right, a pro until he can't perform it wrong", then it's time to take it out and see.

What do other people do?