In the Top Shot competition, during the first episode, where they were shooting the pool balls I was amazed about how crappy they were shooting. These shooters were way better than this.
We were chatting about it at work and our theory was that the run just before they shot put them off. All it takes is a small change in a shooters breathing, a small shake of the hand. Anything that changes up the conditions. I think when you combine this with time pressure you get misses.
It illustrates that you need to practice in all kinds of conditions. Tired, cold, hot, sleepy, buzzing on caffeine or adrenaline, standing, sitting, moving, light, dark, anything really.