Thoughts on the new year

I am easily managed,
you must merely be firm with me,
show 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, but I work with all the precision
of a machine, plus the intelligence of a person.
Now you may run me for ruin. It makes me no diffrence to me.
Take me, train me, be firm with me, and I will lay the world at your feet.
Be easy with me and I will destroy you.
Who am I ? I am called a habit.

Author unknown.