Why did Christopher Reeve wonder, "What else is there left for Superman to do that hasn't been done?

Verified Answer :

Christopher Reeves was always remembered for portraying the
DC superhero Superman as well as a number of roles in movies, television and
stage. Yet it was when he suffered a riding accident that left him paralyzed
that he showed the world he was truly a Superman.  Reeves concentrated his energy on medical
research for spinal injuries that benefited not only him but others.  He continued to push for more research in
government until his death.  He has done
a lot yet even in the end, he felt there was more to do despite his
difficulty.   Even in real life, he truly
was Superman.