You should not use a sharpened knife or scissors for cutting sandpaper. You only blunted their blades. Easier and more effective to cut the sandpaper with an awl or other sharp object on the underside of the abrasive surface and tear the paper along the planned lines.
Recommend to read
SECRETS OF THE OLD PAINTER
Usually on the surface of stored paint forms a film or crust, when removed often remain in the container its particles: once on the brush, they can spoil the work. Take the time to look...
AND VANE, AND A SCARECROW
It is known that the established garden weathervane with propeller with its constant sound and vibration that is transmitted through the pole into the ground, drives away from the area...
