They discover that the hair still comes free in the direction of the now trimmed tip, not the root end. This graphically demonstrates the presence and direction of the scales. Hold another clean Mule Deer hair firmly by the tip adjacent your ear. You will be able to hear the squeak of the scales as your fingers catch against them. If your reverse the hair end for end and repeat the process, there will be silence as your fingers slide over the scales in a direction of no resistance.
Scales have interplay in various aspects of fly tying.
Scales on hair provide numerous disadvantages and few advantages for the fly tier. More will be discussed with specific materials, but one item is appropriate to mention here. The resistance of individual hair's scales against adjacent hairs slows the stacking process. To verify this take a clump of clean bucktail and attempt to stack it. After 2 or 3 taps with the stacker observe your results.