The endowment effect isn't a fixed, universal law of the mind — it can be substantially trained away by market experience. Novice traders show the classic pattern (reluctant to trade an item they've just been given for an equally valued alternative), but frequent, experienced traders show little to no endowment effect at all, treating possessions more like interchangeable units of value than like extensions of themselves.
This matters because it reframes the endowment effect as a default, not a destiny: repeated experience specifically in a trading context appears to teach a more purely economic mindset toward possessions, at least within that specific domain, even though the same experienced trader likely still shows a full endowment effect for possessions outside their area of practiced expertise.
Economist John List studied real collectors at baseball-card and sports-memorabilia conventions, observing their actual trading behavior rather than running an artificial lab experiment. Novice traders showed the classic endowment effect clearly: reluctant to trade away an item they'd just been given for an equally valued alternative item, even when there was no practical reason to prefer one over the other. Experienced, frequent traders showed almost none of this reluctance, trading readily whenever a deal made sense on its merits, much closer to the frictionless behavior standard economic theory would predict.