Borrowing methods across markets, and where it stops working

Pleased to see the last few posts pulling ideas from a market none of us trade. That's usually where the good material is — a different market forces different habits, and the habits travel even when the instruments don't. A caution from someone who has done this badly. What transfers is method: how to normalize a measure, how to structure a ranking, how to name a defect so people stop arguing about it. What does not transfer is anything downstream of market structure, settlement rules, price limits, who the participants are, what the tax treatment does to holding periods. The failure mode is subtle. You import a technique that worked over there because of a structural feature you didn't notice, apply it here where that feature is absent, and get a result that's plausible but hollow. It won't announce itself; it'll just quietly underperform. So when you borrow, ask what in that market makes the technique work, and check whether that thing exists here. If you can't name the mechanism, you've borrowed a superstition. Stay humble.