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 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 individuals 
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 human being. 
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