I want to be a confident writer

JA Konrath of A Newbie's Guide to Publishing lays out the difference between confident and delusional writers. I'm certainly not delusional, but I'm not confident, either. I have an insecurity complex the size of a gas giant. Sadly, being insanely self-critical has led to much of my career success, but it's also holding me back. Switching from self-defeating perfectionism to self-empowering confidence without indulging in delusion is going to be difficult, but if it was easy, anybody would do it.