Community Discussion Question: Biggest Prospect Disappointments

Here is a discussion question to get you started today: in the time you have been a baseball fan, who has been your biggest prospect disappointment? Why, in your view, did the guy fail?

Injuries are obviously a frequent factor here, especially for the pitchers, so try and come up with some names of players who didn't have significant injuries but disappointed you anyway.

I'll weigh in with my own ideas in the comment thread.