Answer:
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 breath on this terrestrial ball.
I'm not man's best friend, I'm their enemy, I can mark your end, yet you do not see me, I am very small, but very tough, If you have me, then you have it rough.
Gets rid of bad ones, short and tall. Tightens when used, one size fits all.
At night I come without being fetched. By day I am lost without being stolen.
What is it which builds things up? Lays mountains low? Dries up lakes, and makes things grow? Cares not a whim about your passing? And is like few other things, because it is everlasting?
If lightning strikes an orchestra who is the one most likely to get hit?