Catherynne M. Valente - When you are born, the golem said softly, your courage...

When you are born, the golem said softly, your courage is new and clean. You are brave enough for anything: crawling off staircases, saying your first words without fearing that someone will think you are foolish, putting strange things in your mouth. But as you get older, your courage attracts gunk and crusty things and dirt and fear and knowing how bad things can get and what pain feels like. By the time you're half-grown, your courage barely moves at all, it's so grunged up with living. So every once and a while, you have to scrub it up and get the works going again or you'll never be brave again. Unfortunately, there are not so many facilities in your world that provide the kind of services we do. So most people go around with grimy machinery, when all it would take is a bit of spit and polish to make them paladins once more, bold knights and true.