I personally think the old song about you should be able to pass down a good knife to the next generation is pure myth. Basic sharpening is also slowly destroying any blade. So how much blade wear does it take before you personally retire it? On paring and western boning knives I'm willing to sharpen them down to a splinter. Chef knives, on the other hand, I retire after they have 10 or 15% blade wear because I feel they aren't the knife I bought anymore. I think I have three 10-inch chefs and one 6-inch chef that I have retired for this reason. They are still knives and could be used for many things but not what I originally bought them for.