Imagine the accuracy from the cut from a rigid Japanese knife. If you would try this with a flexible fish knife you wouldn’t be able to have a clean-cut at all. The rigid knife makes contact with the skeleton ( you hear it) and doesn’t have any bounce-flex at all.

Think of it like this: a flexible fish knife when it encounters and resistance from the skeleton, the force of your hand, and the knife against the skeleton makes the knife bend. When it bends it moves away from the area of cutting area. Some chefs think that the design of a flexible knife is better because of this. But in fact, the knife when it flexes, it bounces and moves wherever it can (given the tension) and cuts the flesh in areas where it shouldn’t. The rigid knife leaves very little room for bounce-flex and it does what you ask it, depending on your skill. When it comes to accuracy a single edge will deliver a more precise cut every time. That’s why a doctor’s scalpel is rigid.