Answer:
This is needed both for courage and hardcover books.
Whoever makes it, tells it not. Whoever takes it, knows it not. Whoever knows it, wants it not. What is it?
Two little holes in the side of a hill. Just as you come to the cherry-red mill.
I'm a god. I'm a planet. I measure heat.
You must keep this thing. Its loss will affect your brothers. For once yours is lost, it will soon be lost by others.
The more of me you take, the more I appear behind you. What am I?