this is great advice, and the comments about your eye deceiving you are right on. i will share this: yesterday, i was practicing from my ladder stand on my 3-D Rinehart deer. on one shot, at about 18 yards and slightly quartering away, i was sure that i saw the arrow fly low, and ricochet off the "belly" of the target and into the ground below.
it wasn't until i got down and walked all the way to the target, that i realized the arrow had actually hit an inch below the heart, in the foam of the leg (a perfect heart shot if the deer even flinched, which they always do). the point is, even on a stationary target, the movement of the arrow and the picture in our mind can cause us to see something other than what occurred.