Answer:
This is needed both for courage and hardcover books.
I cost no money to use, or conscious effort to take part of. And as far as you can see, there is nothing to me. But without me, you are dead.
One by one we fall from heaven down into the depths of past, And our world is ever upturned so that yet some time we’ll last.
Three lives have I. Gentle enough to soothe the skin. Light enough to caress the sky. Hard enough to crack rocks.
All about the house, with his lady he dances, yet he always works, and never romances.
What is so fragile that saying its name breaks it?
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?