"Expert judgment is context-sensitive and degrades when removed from practice.
Read the quote as instruction, not as comfort. In a Sev2 that might become a Sev1, the word sensitive is where the cost hides. If you miss it, you will pay it later.
In a Sev2 that might become a Sev1, the failure mode is rarely ignorance. It is choosing as if the system were simpler than it is, then being surprised by the interaction effects. You see it in a decision kept alive because changing course feels like failure. Name what you are refusing to optimize, so future changes do not quietly destroy the property you thought you were protecting.
Harry Collins is a reminder to keep it concrete. Write the stop line now: what evidence ends the attempt, and what you will do when it appears. Keep it short enough to remember under stress.