Who am I?

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 just 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 all the precision of a machine, plus the intelligence of a person. Now, 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