Reading a great book by Mark Batterson called In a Pit with a Lion on a Snowy Day.
He tells a story about how his doctor, to help him overcome allergic asthma, pricks him with 15 different allergens. She did this because immunity comes from exposing him to small doses of his allergen.
He goes on to explain that fear is the same way. The best thing that can happen to us if we are fearful is to be exposed to small doses of our fear. This builds up immunity. When we encounter our deepest fears we realize that they are not that bad after all. Our fear is worse than the actual thing we are afraid of. We realize it's not the end of the world.
I couldn't help but think of how this rings true in evangelism. One of the greatest reasons people fail to evangelize is fear. Fear of failure, fear of rejection, etc.
What we can learn from this example is that our answer is in facing our fear.
When we step out to share Christ with others, our experience of rejection and failure will bring immunity so in the future we can be more and more effective leading people to Christ.