_It

It doesn't care what you think, what you want, or who you think you are.

It is relentless, unforgiving; it will not let you rest.

You can't get away from it no matter how hard and fast you run.  Oh, you can create some temporary distance once in a while, but it will sneak back up on you and stare you right in the face.

Hopefully, if you live your life right, in time you will come to be at peace with it; accept it for what it is, make friends with it, and become comfortable living with it. 

Then you can leave this place in peace.

What is it?

It's you, of course.