esse when you sharpen a blade with a coarse stone it leaves tiny grooves in the edge the width of the stones grit,because of the shape of the grit is roughly spherical the edges of the grooves are sharp and when the hair is caught by the groove it cuts on this edge(think microscopic saw blade) when you progress to a finer stone it's grit is closer together so it squashes the ridges between the grooves but with more strokes it creates it's own grooves,this process continues as you go to finer and finer grits,sand paper shows the progression of grooves really well and cutting certain things with a knife sharpened on a really low grit you can feel it grab,it's just how sharpening works