Riddle

We heard this riddle last week and wanted to share it with you:

I am your constant companion. I will push you forward to success or I will drag you down to failure. I am completely at your command. 80% of what you do, you might as well hand over to me and I will do it promptly and I will do it correctly. I am easily managed; you must merely be firm with me. Show me what you’d like to have done, and after a couple of lessons, I will do it automatically. I am the servant of all great people. Alas, I am the servant of all failures as well. All who are great, I have made great. All who are failures, I have made failures. I am not a machine; but I do work with the precision of a machine and the intellect of a human. Take me, train me, be firm with me, and I’ll lay the world at your feet. Be easy with me, and I will destroy you!

Who am I?

You can get the answer here. We thought the comments included with the answer were also interesting.