What makes a good knife? Of course, a good knife is a knife that cuts well.
But what does it mean to cut well? Just the sharpness of the blade? What about grip comfort? And balancing? And stickiness? And weight? And what about the thing being cut? Can a knife cut everything well?
As you can see, we are already dead in our tracks, as asking what makes a knife good is basically on the same level of complexity of asking the same thing about a human, and this is why ancient philosophers, many of whom didn't really explore nuance, should be critically studied, without falling for simplistic "this is my hero" behavior