I always think before an important shot: What is the worst that can happen on this shot? I can whiff it, shank it, or hit it out-of-bounds. But even if one of those bad things happens, I've got a little money in the bank, my wife still loves me, and my dog won't bite me when I come home.
Anyone who hasn't been nervous, or hasn't choked somewhere down the line, is an idiot.
Concentrate on hitting the green. The cup will come to you.