Trusting Yourself

I was talking with a friend, a guitarist, and we were discussing his music. Mostly I like his music, but I think that he doesn't stay with his ideas long enough--I think he's got good idea that just need to be given more time in their expression. I suggested this to him and he said (paraphrase) "well, yeah, I should develop the ideas more but, I can't."

I think a lot of us are like this as writers: we have an idea and we give up on the idea saying "I can't develop this idea more."

But for my friend the guitarist, and for many of us as writers, the problem is that we don't stay with the idea long enough. We don't work it and rework it. Instead we play the wrong note, or we lose track of our place in the progression, and having hit that first failure we say "I blew it; this ain't gonna work." But a lot of time it's really that we didn't trust our ability to push through the place of difficulty. It's not that we need to do anything different; we just need to stick with what we are doing longer. We need to trust in our abilities.

Sometimes I think of this situation in terms of two binary variables:
whether we trust ourselves (yes or no)
and
whether we have the ability we need (yes or no)
What combination of these variables will lead to success? There are 4 possibilities:
1. obviously, if we don't have trust and we don't have ability, we're not too likely to succeed.
2. If we don't have ability but we do believe, our chances are better, but still....
3. If we do have ability, but we don't believe, then we have some chance, but we're also likely to hold ourself back.
and
4. If we do have ability and we trust that ability, then we are most likely to succeed.

What is important to note here is that whether or not we have the ability we need, our chance of getting a good outcome is improved by trusting ourself, while there is no increase in risk.
OK, there is a simplification operating here, and there are situations where our risks increase by (unjustly) believing about ourself. But here's the question: are there any situations in which a dissertation writer benefits by doubting his or her ability to do the work? And if there are no such situations, or if those situations are rare, isn't it worth acting on the assumption that your abilities will be up to the effort?