The pencil moves swiftly across the page.
Then you see that you've made a mistake.
This causes the eraser to shrink.
Oops, you've made another mistake.
The eraser is now a little smaller.
Your story, however, is not yet finished.
There will be more mistakes and soon the eraser will be even smaller.
One mistake is all it takes for the eraser to shrink until its finally gone all together.