==> PENCIL: I'm sorry
==> ERASER: For what? You didn't do anything wrong.
==> PENCIL: I'm sorry because you get hurt because of me. Whenever I made a mistake, you're always there to erase it.
But as you make my mistakes vanish, you lose a part of yourself.
You get smaller and smaller each time.
==> ERASER: That's true. But I don't really mind. You see, I was made to do this. I was made to help you whenever you do something wrong. Even though one day, I know I'll be gone and you'll replace me with a new one, I'm actually happy with my job. Soplease, stop worrying. I hate seeing you sad.

Parents are like the eraser where as their children are the pencil. They're always there for their children, cleaning up their mistakes.
Sometimes along the way, they get hurt, and become smaller /older, and eventually pass on.
Though their children will eventually find someone new (spouse) , but parents are still happy with what they do for their children, and will always hate seeing their precious ones worrying, or sad.

All your life, you have been the pencil. And it pains to see the eraser that is our parents getting smaller and older each day. For we know that one day, all that we are left with would be eraser shavings and memories of what we used to have.