You have a person who has an incredible talent, whether it be cooking, writing, sports, whatever. This person briefly showed this talent but then is living their life without fulfilling their calling in life. I would like a noun and I would hope it would not only convey that the rest of the population is missing out on that person's talent too.
Note: The Will Hunting comment is a good one. 1 out of 5 movies seem to be about this type of person.