Answer:
What binds two people yet touches only one?
There is an ancient invention. Still used in some parts of the world today. That allows people to see through walls.
I am free for the taking. Through all of your life, though given but once at birth. I am less than nothing in weight, but will fell the strongest of you if held.
This is needed both for courage and hardcover books.
They belong to me; they belong to you; They can make you feel happy or make you feel blue; They never end until the day you do.
You use it between your head and your toes, the more it works the thinner it grows.