Who am I?

I'm your constant company, your best helper or your heaviest burden
i'll push you forward or crawl you towards failure
i'm completely at your command, you can leave me without problems.

Half of what you do, i'll do it quickly and correctly
is easy to handle me, only you must be firm,
tell me exactly how to do something and few lessons i'll automatically do it.

I serve great men
those are great I have made'em even greater
those who are failures, I have made'em further failure

I'm not a machine,
even when i work with the precision of one,
and with the intelligence of a man or a woman

You can use me to win or you can use me to ruin, for me, I do not care
Take me, use me for first, be firm with me and i'll put the world at your feet
be flexible with me and I will destroy you

Who am I?

Your habit