In so far as theories of mathematics speak about reality, they are not certain, and in so far as they are certain, they do not speak about reality.
I never think of the future. It comes soon enough.
Everyone sits in the prison of his own ideas; he must burst it open, and that in his youth, and so try to test his ideas on reality.
I do not carry such information in my mind since it is readily available in books. The value of a college education is not the learning of many facts but the training of the mind to think.