Over-Sharpening

[KnifeGrinders]

The SEM image courtesy Todd Simpson scienceofsharp.wordpress.com

Imagine you've raised a burr grinding the right side, and now are grinding the left side. Green line is the right amount of sharpening, you get an edge of half a micron, while the red line is oversharpening and you get an edge of several microns. 
Thickness of the edge you get is shown by shorter horizontal lines; the material over these horizontal lines will be shifted to the right as a newly formed burr.

As you move to honing to remove the newly formed burr on the right side, in the end you get either a sharp edge under half a micron (green zone), or blunt end of a few microns (red overground zone).

Oversharpening is more of an issue with double-bevel edges