Why?

It hurts to think too much.
It stresses to love.
It kills to live.
But how come it thrills to hate?

Maybe it's cause we're human?

The pillow is a better friend. It lends a shoulder(metaphorically), and it cannot run away. (even if it wants to)

Isn't that the best 'friend' you have?

It can't bear hatred. It's dead. =)