I've been carrying this around with me every day for a while now. "Memento Mori" It's Latin for "remember death." A lot of people think it is morbid, but it is a powerful motivator. The philosophy dates back to Socrates and Marcus Aurelius. But I think it is best put by the great Stoic Senaca the Younger... "Let us prepare our minds as if we've come to the very end of life. Let us postpone nothing. Let us ballance life's books each day... The one who puts the finishing touches on their life each day is never short of time." Live life to the fullest, take nothing for granted... you could leave life right now.
Hat tip @timferriss