I think one thing you mentioned was the fear coming from an "incomplete trust in God." This I think is true. The best analogy for this is whenever I go swimming. I stick my toe in the water, maybe my leg, feel how cold the water is, pull it out, pace around wondering whether to jump in or not, feeling like if I do I will immediately turn into a block of ice...come close to the edge, get ready to jump, back off, pace some more, make a second attempt, lose my resolve again. Then I stand on the edge and realize I have two choices...jump in, or stand on shore. Even when you wade in the water, at some point you have to put your head in.
There is that moment of terrifying equilibrium when you do decide to jump, when your body leaves the side of the pool and your balance is such that your choice becomes irreversible. You can decide to get out once you're in, but you're on course for getting wet, and not just a little wet, but completely unequivocally submerged. I feel this every time I am in the air. It's like you make a choice, a choice to jump, and there's just a second or so before you feel the full implications of that choice. That is usually the 'oh shit!' moment, like 'oh shit! this is going to hurt!' or 'oh shit, this is awesome!' Different people have different reactions depending on their dispositions. I think the people who enjoy jumping into cold water the most are the ones who don't think about how the water 'might' feel...in fact, they are the ones who don't think about it at all. They feel the cold rush of the water when they feel it...not before, not while they're in the air or on the shore, but all at once.
The funny thing is, once you are in the water, you wonder what all the fuss was about. Sure it is cold, but your body adapts pretty quickly. You move your arms and legs. You are in a new environment, it is cold, but you are alive! You did not die, or go into shock. The more you think about how cold the water "might" be, the less inclined you are to jump at all. In short, more thinking=less action. I guess you can apply this to getting married, moving, making a career move...all that grown-up stuff.