"Sharp" is such a vague word. To me, a blade that is "sharp" will cut hair when you slice at it with its edge. I've thrown away so many blades that were "sharp", because they were not keen. A keen edge gives you close and comfortable shaves. I've found that the majority of blades (maybe all) lose keenness after 6 passes and at that point they are still perfectly good at cutting, just not going to give you the best results possible at all the angles needed to give you a close comfortable shave. A blade will cut hair for many many shaves.I find most blades have two drop off curves. The first is the gradual loss of sharpness. The second is that one day it was doing fine. The next day it was tugging.