The Power Of Habit

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 completely at your command.
 

Half the things you do, you might just as well turn over to me, and I will be able to do them quickly and correctly.
I am easily managed; you must merely be firm with me.
 

Show me exactly how you want something done, and after a few lessons I will do it automatically.
I am the servant of all great men. And, alas, of all failures as well.
 

Those who are great, I have made great.
I am not a machine, though I work with all the precision of a machine. Plus, the intelligence of man.
You may run me for profit, or run me for ruin; it makes no difference to me.
 

Take me, train me, be firm with me and I will put the world at your feet.
Be easy with me, and I will destroy you.

Who am I? 

I am habit.

Author Unknown