A Riddle

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 am completely at your command. Half the things you do might just as well be turned 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 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, though I work with all the precision of a machine plus the intelligence of a person.  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 place the world at your feet.  Be easy with me and I will destroy you. Who am I? I am habit!!

TankDiesel