Patrick Ewing
Ewing was a brilliant player and remains a Knicks icon. However, he ultimately personifies the most frustrating aspects of the franchise. Ewing took the team within touching distance of glory but fell short at crucial moments. One notorious and career-defining moment came in the playoffs against the Miami Heat.
The series went all the way to Game Seven and Ewing had an opportunity to win. The ball came his way and it appeared that he would dunk it. But the clutch situation affected him and the ball rolled away from him instead. This proved costly and ultimately became a career-defining moment (via N.Y. Post).