The NFL has a significant turnover rate, and this can be largely attributed to the turnover rates among players.
Very frequently, players will have had a breakout year, only to have a quiet season shortly after. Or players that are usually dominant and excellent fantasy options are now either aging or being figured out by opponents and successfully game planned against.
Whatever the reason, these players have all failed to live up to their expectations and have caused fantasy owners across the country to tear their hair out in frustration.
For the sake of fairness, I will leave out players who have been injured (such as Peyton Manning and Arian Foster).