The exceptions keep coming

Add a rule for an uneven base.

The next machine shows similar warning signs because a belt is too tight. Add another rule.

Later, a temperature sits too close to a hot pipe and reports heat from the wrong place. Another rule.

Different causes can produce similar clues. The system cannot consider a cause until someone adds it to the rulebook.

The rules grow longer and begin to overlap. A change that fixes one case can alter the path through another. No finite rulebook can anticipate every future case.