Chesterton's Fence

The proportion of conditional outcomes exercised — the strictest ordinary coverage metric, and the most informative.

The number of people who would have to leave before a project stalls.

Imitating the visible form of a practice while the mechanism that made it work is absent.

Prose inside source code, useful only when it records a constraint the code cannot state.

A substituted value that papers over a missing input and hides the misconfiguration that produced it.

Documentation that has drifted from the system it describes, and is now worse than none.

Repeatedly asking why a symptom occurred, chaining each answer into the next question until the causal chain runs out.

With enough users, every observable behavior of an interface becomes a dependency for somebody.

Making a system countable and administrable, at the cost of the local knowledge that made it work.

Choosing identifiers so the code states its own meaning without commentary.

Outcomes shaped by the sequence of past choices rather than by present merit.

A causal explanation that was inferred rather than tested, and reads as more rigorous for being specific.

Escalating past the visible symptom until you find the layer that actually produced it.

The future cost of a present shortcut, metaphorically accruing interest.

Code no input can execute — usually a guard against a state the surrounding invariants forbid.

Asking for help with your attempted solution (Y) instead of your actual problem (X), so the help solves the wrong thing.