It is the mark of an educated mind to be able to entertain a thought without accepting it.
Aristotle
The aim of education should be to teach us rather how to think, than what to think — rather to improve our minds, so as to enable us to think for ourselves, than to load the memory with thoughts of other men.
Bill Beattie
If my mind can conceive it, and my heart can believe it— then I can achieve it.
Muhammad Ali