Keys to Success Pt IV

I am your constant companion.
I am your greatest helper or heaviest burden.
I will push you onward or drag you down to failure.
I'm at your command.
Half the tasks at you do you might as well turn over to me, and I will do the quickly and correctly.

I am easily managed. You must merely be firm with me.
Show me exactly how you want something done.
After a few lessons, I will do it automatically.
I am the servant of all great people and alas of all failures as well.
Those who are great, I have made great.
Those who are failures, I have made failures.

I am not a machine, but I work with all the precision of a machine, plus the intelligence of a person.
Now you may run me for a profit or you may run me for ruin,
It makes no difference to me.
Take me, train me, be firm with me, and I will lay the world at your feet.
Be easy with me and I will destroy you.

Who am I?

I am called HABIT.

- Author unknown