from Frank Wilczek's Nobel (physics) lecture, 2004 ("Asymptotic Freedom")

[fflo]

In theoretical physics, paradoxes are good. That's paradoxical, since a paradox appears to be a contradiction, and contradictions imply serious error. But Nature cannot realize contradictions. When our physical theories lead to paradox we must find a way out. Paradoxes focus our attention, and we think harder.