Warren in Lancaster, PA
On a rainy Sunday in May I watched four or five U-tube videos of guys making half blinds. They all started out saying a very sharp chisel was essential; they all abused the chisel so much in the first minute that it was no longer sharp.

Chisels that are struck cleanly wear with abrasive wear. Chipping and rolling come from shear and bending forces: prying, twisting, scraping, digging. A lot of guys will hit the chisel in then flick out the waste, not realizing they are scraping the edge. Or they will hold the chisel near the bevel, not realizing that when the handle flops around with the chisel in the cut there are bending forces on the edge. Or they will get the chisel stuck and yank it out rather roughly. Few intentionally abuse the chisel, but sloppiness inadvertently causes edge damage. It can be pretty subtle.