A man, as a general rule, owes very little to what he is born with - a man is what he makes of himself. 
Before anything else, preparation is the key to success.
Concentrate all your thoughts upon the work at hand. The sun's rays do not burn until brought to a focus.
Great discoveries and improvements invariably involve the cooperation of many minds. I may be given credit for having blazed the trail, but when I look at the subsequent developments I feel the credit is due to others rather than to myself.
Man is an animal which, alone among the animals, refuses to be satisfied by the fulfillment of animal desires.
Sometimes we stare so long at a door that is closing that we see too late the one that is open.
What this power is, I cannot say. All I know is that it exists...and it becomes available only when you are in that state of mind in which you know EXACTLY what you want...and are fully determined not to quit until you get it.