The Republic - pg. 154

"Unless," I said, "the philosophers rule as kings or those
now called kings and chiefs genuinely and adequately
philosophize, and political power and philosophy coincide
in the same place, while the many natures now making
their way to either apart from the other are by necessity
excluded, there is no rest from ills for the cities, my dead
Glaucon, nor I think for human kind, nor will the regime
we have now described in speech ever come forth from
nature, insofar, as possible, and see the light of the sun.
This is what for so long was causing my hesitation to speak:
seeing how very paradoxical it would be to say. For it is
hard to see that in no other city would there be private or
public happiness."