Self-confidence or Presumption?

What is the difference between self-confidence and presumption?  How do I have true humility and also the confidence to promote my work?

As I wait to hear from another editor, this is the issue that again I wrestle with.  For some reason, when it come to my writing, I've always needed a lot of reinforcement from people around me.  If I don't have people telling me that they like my books, that they were meaningful to them, it's hard for me to believe that they are any good or that my writing is worthwhile.  Or maybe I feel that I'm wasting my time if no one is going to read my books anyway.

I suppose this is a personality issue, at least partly.  I've read books that I really didn't think were all that good, and yet clearly their authors had enough self-confidence to go through the painful process of publishing.  In the process, they found an audience:  a group of readers who enjoyed their books enough to shell out the money (or at least go to the library) and spend the time in the imaginary world the author had created. This seems like presumption to me, but maybe it's really just healthy confidence.  And, of course, different audiences enjoy different types of writing, and what seems like trash to me might be thoroughly enjoyable to someone else.

In The Screwtape Letters, C.S. Lewis talks about pride and humility, and the true purpose of humility:  "Let him think of [humility] not as self-forgetfulness but as a certain kind of opinion (namely, a low opinion) of his own talents and character.  Some talents, I gather, he really has.  Fix in his mind the idea that humility consists in trying to believe those talents to be less valuable than he believes them to be.  No doubt they are in fact less valuable than he believes, but that is not the point....[God] wants him, in the end, to be so free from any bias in his own favour that he can rejoice in his own talents as frankly and gratefully as in his neighbour's talents."

Alas, I am not there yet.  I fear I am a long way from that true type of humility, and I wonder if I will ever get there.  I want to be told that my writing is good and meaningful, but even when I hear that (as I have, many times - one of the women in my writer's group told me I should look in the mirror every day and tell myself, "You have a really good book here!"), it never completely satisfies me.  Perhaps the reason that I want to be published so badly is that I see it as that final validation:  Some professional actually thought my writing was good enough to take a chance on.  But since I know that professionals often take a chance on writing that really isn't good at all, why should that matter so much?

I am bracing myself for another rejection and wondering how I should react to it.  I know my initial reaction will be that I will never want to try again.  I have never gotten this close before, I don't believe I will again.  But should I be happy to continue writing without any real audience except the circle of loyal friends who have been my readers for the last 18 years?  Or should I try the self-publishing route - which demands more self-confidence (or presumption) than I have ever yet managed to find in myself?

These are the questions that I wrestle with as I wonder and wait.