Who Am I?

I am your constant companion.
I am your greatest helper or your heaviest burden.
I will push you onward or drag you down to failure.

I am at your command.

Half of the tasks that you do, you might as well turn over to me, and I will do them 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 the precision of a machine plus the intelligence of a person.
You may run me for 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