One day a disciple asked his teacher, 
"Teacher, what's the difference between living virtuously and not living virtuously?"
"If they are compared with each other, the person who lives virtuously is like a crescent moon and the person who does not live virtuously is like a moon after the full moon."
"Please explain that to me."
"A full moon will afterwards be waning more and more, and finally all the light will disappear. But a crescent will get brighter and brighter and finally moon will shine all over the world."

From the discourses of the Buddha