From The Alchemist:
The camel driver, though, seemed not be very concerned with the threat of war.
"I'm alive," he said to the boy, as they ate a bunch of dates one night, with no fire and no moon. "When I'm eating, that's all I think about. If I'm on the march, I just concentrate on marching. If I have to fight, it will be just as good a day to die as any other.
Because I don't live in either my past or my future. I'm interested only in the present. If you can concentrate always on the present, you'll be a happy man. You'll see that there is life in the desert, that there are stars in the heavens, and that tribesman fight because they are part of the human race. Life will be a party for you, a grand festival, because life is the moment we're living right now."
"don't worry, be happy"