The "World of Cardboard" Speech:
"That man won't quit as long as he can still draw a breath. None of my teammates will. Me? I've got a different problem. I feel like I live in a world made of cardboard, always taking constant care not to break something, to break someone. Never allowing myself to lose control, even for a moment, or someone could die. But you can take it, can't you, big man? What we have here is a rare opportunity for me to cut loose and show you just how powerful I really am."
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For those interested, I've expanded and annotated
The Top Five Superman Stories list.