Andrew Luck
Some might say that Luck deserves to be higher on this list. But his story is one of unfulfilled potential because he retired in his prime. The Colts gave up Peyton Manning after his injury-struck year because Luck fell into their laps. It was incredibly lucky because the Stanford star was brilliant (via The New Yorker).

The four-time Pro Bowler won the NFL Comeback Player of the Year award in 2018. He led the league in passing touchdowns in 2015 as the Colts rubbed their hands together gleefully. But he stepped away after seven seasons because of his injury record. Arguably, the Colts never saw the best of him and that’s a shame because they never protected him.