There are pretty much two types of deer hunters; those that have unfortunately lost a wounded deer and those that will.....
Tough to figure that any animal shot "perfectly" would not be found after a reasonable trailing job. Rather, you might figure that your perfect sight picture at trigger pull was affected by one of several factors such as an unseen branch between muzzle and target or a deer that moved just as you squeezed the trigger, just to name a couple.
All ethical hunters regret such occurances and strive to do all they can to reduce the chance of something similar happening again. Trailing a wounded deer is a whole nother skill that needs to be added to a good hunter's skill set. You, however, can only practice it after a deer that's be shot moves off out of sight.
Best of luck on all your future hunts!