The field guide · rule 03 of 16
Decide what happens when things break
When part of a system fails, choose whether it stops or carries on, by asking what a wrong answer would cost.
What it means
When something goes wrong, a system can stop, or it can carry on doing less. Choose by asking what it costs to be wrong. If the risk is losing money or leaking data, stop. If the risk is a report with one figure missing, carry on and say so.
What goes wrong without it
A payment check times out and is treated as "paid", so someone gets access they never paid for.
How I build it
- In my AI agent system, if the spending meter cannot be read, every AI call is refused. If an AI answer cannot be read, the job carries on with an empty result.
- In my chain-intelligence service, if the database cannot confirm that a payment has not been used before, access is refused rather than risk giving it twice.
- My mining apps install nothing if a download's fingerprint is missing.
Ask your team
- For each important step, do you know whether it stops or carries on when something fails?
- Does anything that touches money stop when it is unsure?
- Do people see a clear message when a part is unavailable?
How a review checks this
A review walks through what each important step does when the step before it fails, starting with the steps that touch money.
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