"It is important to maintain your equanimity. You cannot let yourself get too 'up' or too 'down' based on your circumstances."
"Too 'down' I understand. But why not too 'up?'"
 "Because the higher your mountains are, the deeper your valleys will seem. You should not react to the world.
You should respond, but not react. A response is an action based on logic. A reaction is an emotional state. Your reaction will not change the world.
Your reaction only changes you. Your response will change the world."

Taken from Humans of New York