A check is worth doing only if its result could change the decision. Checking where an error is cheap and reversible, or checking what changes nothing, looks like diligence and produces no result.
Stakes are two independent questions: what happens if the answer is wrong and I rely on it, and can I fix it when I notice. A wrong date in a sent letter is cheap and irreversible; a month spent in the wrong direction is expensive and reversible. Both errors are symmetric: accepting an answer where error is costly, and verifying where it is not. Artificial urgency — a deadline, a “today only” — makes a two-way door look like a one-way one; ask whether a smaller reversible step (a pilot) answers the same question.
The model never stops by itself — there is always one more reasonable check to propose. Stopping is the human’s decision, and it is the moment responsibility becomes a fact: someone says “enough, act” and signs. The same logic as Reversible vs irreversible decisions and Human-in-the-loop for irreversible actions.
Where it comes from. Decision analysis made this precise: Ronald A. Howard, “Information Value Theory” (IEEE Transactions on Systems Science and Cybernetics, 1966), defines the value of information as the difference between the expected value of the best decision with it and without it. Information that cannot change the decision is worth exactly zero, however interesting. The door metaphor is Jeff Bezos’s: his 2015 letter to Amazon shareholders separates Type 1 decisions, one-way doors that deserve slow care, from Type 2, two-way doors that should be made quickly by small groups.
An engineering example. A model’s claim about a config default behind a feature flag is cheap and reversible: try it on a canary (72). Its claim that a migration may drop a column, or that last night’s backup restores, is neither — that one is checked by a restore and a read of the code path, not by asking again (20, 97).
Limits. Howard’s formula needs probabilities you rarely have, so in practice it orders checks rather than prices them. And irreversibility hides: a sent email, a published key or a deleted row looks like a two-way door until you try to walk back through it.