Rule 16 of 27 · Chapter IV — The Knife and the Cut
Keep your knife sharp
Why this rule exists
A sharp knife is safer than a dull one, which surprises people until they think it through. A sharp blade bites where you place it and glides through with light pressure, so it goes where you aim; a dull one skids off the food's surface, requires you to push hard, and slips, and it is that slip, driven by force, that opens up your thumb. Beyond safety, a sharp knife makes prep faster, cleaner, and more pleasant, cutting through a tomato or an onion instead of crushing it, which keeps flavor in and mess down. Most home cooks work with knives that have not been properly sharpened in years, blame themselves for clumsy cutting, and would be transformed by ten minutes of maintenance. The knife is the tool you touch most; keeping it sharp is the highest-return habit in the kitchen.
In practice
Hone the blade with a steel or rod before or during each session to keep the edge straight, and understand that honing is not sharpening. Sharpen properly on a whetstone or with a good pull-through or a professional service every so often, when honing no longer restores the bite. Test sharpness on paper or a tomato skin, not your thumb. Wash and dry knives by hand rather than in the dishwasher, which dulls and damages them, and store them protected in a block or on a magnetic strip, never loose in a drawer where they knock against everything. One good, sharp knife you maintain beats a block of dull ones.
When it doesn't apply
Serrated knives, for bread and tomatoes, are sharpened differently and much less often, mostly just replaced. Very hard Japanese steel holds an edge longer but chips more easily, so treat it gently and avoid bones and frozen food. And there are jobs, like hacking through squash or bone, for which you want a sturdy cleaver, not your fine chef's knife.