I believe that confidence comes when you are willing to go through with something even if you could possibly be wrong. Taking that fear element and putting it in it's proper place is the first step.
Most people don't develop the confidence they need to succeed because of being afraid of how others will react or fear of failing. I'm sure you have heard the definition of "fear"... False Evidence Appearing Real. You have been fooled into believing that if you step out and face your fear to accomplish your goal, you will fail. Your mind runs wild and you begin to believe those nay-saying voices telling you, "you'll never amount to anything."
You have to turn off those voices by replacing them with scripture that speak strength and courage into your life. When you replace the fear with strength and courage, you will have the confidence you need to face any situation that comes your way. The entire book of Psalms 27 is excellent to keep marked in your Bible. The first verse says...
"The Lord is my light and my salvation--
whom shall I fear?
The Lord is the stronghold of my life--
of whom shall I be afraid?"
And my favorite scripture comes from Psalms 27:13-14...
"I remain confident of this:
I will see the goodness of the Lord
in the land of the living.
Wait for the Lord;
be strong and take heart
and wait for the Lord."