Unfortunately, that comes with the territory. I know the feeling, and have beat myself up mentally when it has happened. At some point, even the most seasoned archer will have a mishap/bad shot. Could be attributed to many things even when we think it was "Perfect". Did the limb catch on something? Did the string catch your sleeve slightly? Was the arrow seated on the nock? Was a vane/fletching torn or loose? So many little things outside of our immediate awareness could happen.
Complacency/over confidence of the "Perfect shot setup".

Situations like that forced me to sharpen my skills even further and to constantly work on them. I can't say it won't happen again, because if you spend enough time in the field, it will. Like stated above, that animal will not go to waste. I firmly believe everything happens for a reason. In the greater scheme of things, what happened was meant to happen.