Men give me some credit for genius.  All the genius I have lies in this: When I have a subject in hand, I study it profoundly.  Day and night it is before me.  I explore it in all its bearings.  My mind becomes pervaded with it.   Then the effort which I make is what the people call the fruit of genius.  It is the fruit of labor and thought.

Thinking is the hardest work there is, which is probably the reason so few people engage in it!