Sandpaper is rough on purpose. Some people in your life are there to smooth your edges.

Friction from someone who wants you to be good at this feels bad in the moment and different an hour later. The coach who calls your defense lazy, the friend who says that text was out of line. Rough is doing the work, and it never feels like care while it is happening.

Judge it by what is left afterwards: sharper, or just smaller. Someone who only ever leaves you smaller is not sandpaper. You are allowed to stop handing them the wood.