Here's an excerpt:
Confidence allows for fallibility and flexibility, and therefore helps you to develop trust with your audience. Think of the sometimes off-putting perfectionism and certainty of Martha Stewart, versus the humility and benevolent confidence of Oprah Winfrey....
Madeline Albright said, "Certainty comes from believing we have learned all there is to know. Confidence comes from the effort to learn all we can."
And here's a link to the entire short piece.