Unfairness of BUST tags...

I think the word/term "bust" is thrown around to easily, when exactly can a player be recognized as a bust? when he's outa the league after 3-5yrs after being so highly touted? or if he has a 12yr career but never lived up to his hype?....or is it when fans are upset that a player isnt playing, so he must be a "bust"? who determine's this? and exactly when should this be determined? after 2yrs....3, 4 or 5?