The test of a first-rate ...

The test of a first-rate intelligence is the ability to hold two opposed ideas in mind at the same time and still retain the ability to function.
The test of a first-rate intelligence is the ability to hold two opposed ideas in mind at the same time and still retain the ability to function.

More phrases

If one does not know to which port one is sailing, no wind is favorable.
What a distressing contrast there is between the radiant intelligence of the child and the feeble mentality of the average adult.
We are masters of the unsaid words, but slaves of those we let slip out.
I have always found that mercy bears richer fruits than strict justice.
A lie gets halfway around the world before the truth has a chance to get its pants on.

Quotes from the same author

When a man is tired of life on his 21st birthday it indicates that he is rather tired of something in himself.
Thirty--the promise of a decade of loneliness, a thinning list of single men to know, a thinning brief-case of enthusiasm, thinning hair.
mother says that two souls are sometimes created together and--and in love before they're born.
Never confuse activity with action.
I think they're very attractive,' Abe agreed. 'I just don't think they're attractive, that's all.