Who am I?

I found this quote to be inspiring and thought I would share. The author is unknown. 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 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...