I came across this great illustration by Dan Miller:
Let me give you an example: Imagine for a moment that your 3-yr old daughter slipped and fell into the pool while playing. You’ve never had swimming lessons, you don’t know the tempurature of the water, you don’t know how deep the water is where she went in, and you aren’t sure that the suit you have on would withstand the effects of the chlorinated water. Are you going to do some research on each of those issues before acting? Of course not – you’re going to jump in immediately. At that instant you know that doing is more important than knowing.
Same with sales prospecting! Start doing it immediately! You’ll make mistakes but you can tweak and refine it as you go along!