"I can creep up on you in an instant and change your mood.
I can lift you up. I can drag you down.
I have the ability to make you doubt yourself.
I can cause you to cry.
I can give you a boost of energy or I can discourage you.
I am so powerful I can create in you a great purpose
But, often I will point out all the reasons why you will fail.
I am such a big part of you that you just go about your day taking me for granted.
This is not good - not good at all, because I can do so much for you,
If you would just let me.
But, know – I am at your beck and call
My job is to follow not lead.
I always give what you request.
What Am I?"