I am the reason you run, because I allow it. I am the reason you scream. I am the cause of all your pain. I am a cage from which you will never be free.
I never was, am always to be,
No one ever saw me, nor ever will,
And yet I am the confidence of all,
To live and breathe on this terrestrial ball.
What am I?
It can't be seen, can't be felt, can't be heard and can't be smelt. It lies behind stars and under hills, and empty holes it fills. It comes first and follows after, ends life and kills laughter. What is it?