Darwin put it as “ignorance more frequently begets confidence than does knowledge” and now a report titled Unskilled and Unaware of It: How Difficulties in Recognizing One’s Own Incompetence Lead to Inflated Self-Assessments (pdf) says “the skills that make you competent are the same skills that help you recognise competence.”
So could one argue that feeling less than competent is a sign of competence? Via The Age.