Man exhausts himself by two acts, instantly accomplished, which dry up the sources of his existence. Two words express all the forms that these two terms causes of death can assume: will and power. Between these two terms of human action there is another formula which wise men cling to, and to it I owe my happiness and long life. The exercise of the will consumes us; the exercise of power destroys us; but the pursuit of knowledge leaves our infirm constitution in a state of perpetual calm. So desire or violation is dead to me, killed by thought.