Every creature has individual differences. They are both visible and also invisible to the human eye. Take a bass plug for instance, characteristic difference in a plastic plug are a result of an error in mass production. However, a visible characteristic difference in a hand-made plug adds more unique individualism.
In a process where the plastic is injected into a mold, it is under the absolute condition that it produces perfect duplicates by the same shape and color. However, in hand-made lures, while preserving the image of a fish, subtle differences are born as a result of one craftsman's hands on process from design to completion. Just as there are characteristic differences among same species of fish, in a hand-made lure, the subtle difference becomes the characteristic and becomes unique to that lure.