Imagine how frustrating it is for a player with all pro talent to not just not win but to suffer through years of utter mismanagement and starting over every couple of seasons. Brady has addressed how each season is such a battle and that is why he always got so emotional at the ring ceremonies. Unless you're playing for one, or the next one, it must be increasingly difficult to motivate yourself to submit to the grind, mentally as well as physically, year in and year out - no matter how much you love the game or even the paychecks that go with it.
If the Bills were smart they would approach him now about facilitating a trade in the off season. They aren't going to contend any time soon even in their own division.