I find A big reason for a miss, is not picking a small spot, but there is another part to the equation to misses. That is follow through. Its very easy to not pick a spot, but its even more easy to lift your head to try and see the hit. Once the head comes up, the arm goes down and to side. Instead, see the hit happen from the same perspective as you release from. In both of these cases, we've likely practiced it at a target hundreds of times. The notion that it will all just magically transition over to a live deer is a little off base. The fact is, you have to make those attempts and practice the shot on live deer. And No matter how we feel with the rush of adrenaline, to execute both picking the spot, and properly following through the shot. Without real animals to give you the real feelings that come with it, its all but impossible to overcome. It must be experienced, to get better at doing it. Its about how much self disipline you can excersise, and do what you know to do, while under the throes of the moment.
Ive said for years killing deer takes two hurdles to jump that are each complex in nature, that must be overcome. One, get the deer in front of you for a shot opportunity. Two, get the deer dead. Neither come easy, but both are easy to read about and say.