Lyda Morehouse and I were talking about confidence a few days back. Most writers experience a lot of negative feedback: rejections, bad reviews, no reviews, getting dropped by a publisher... The list goes on and on. As a result, it really helps to believe in yourself, to have self-confidence, to have a cast-iron ego.
This is one of these statements which is important without being profound. Yes, of course, people need self-confidence.
There has to be a limit to self-esteem. If you are arrogant, you will piss people off, and you may make career mistakes. In addition, excessive self-esteem may blunt your critical sense. You can't see what about your work needs improving.
The question is, how to achieve balance: to have enough self-confidence to keep going, without becoming a maniac. I don't have an answer. I would say I don't have enough self-confidence, though somewhere in the back of my mind -- in a small, secret room -- I do think I am a wonderful writer. But the rest of my mind contains a lot of self-doubt.
This is pretty common for writers. It's a line of work that encourages mood swings, from the highs of a good writing day or a good review to the lows of rejection and writing that isn't going well.
I was helped by having a father who was an art historian. To a great extent, the important European artists of the later 19th and early 20th century -- the Impressionists and Post Impressionists, the Cubists and so on -- were badly reviewed and did not sell well. My father said once, "Given the history of the last hundred years, no critic should take himself seriously." The critics were almost entirely wrong. When I have trouble selling, I can remind myself that van Gogh sold one painting in his life.
To me, it seems obvious that commercial success is not evidence of merit. So what is evidence? One has to trust oneself.