Endowment Effect

The cognitive bias where people value things they already possess more highly than identical things they don't—simply because they own them. Kahneman's experiments showed that people given a coffee mug demanded roughly twice as much to sell it as people without the mug were willing to pay. The mechanism is loss aversion applied to ownership: selling something you own is framed as a loss, while buying something you don't own is framed as a gain—and losses loom larger than gains. The endowment effect explains why people overprice their homes, resist trading suboptimal strategies, and hold losing investments too long.

When to use it

When assets or positions are being held beyond their rational value; when asking prices vastly exceed market value for owned items; when the 'clean slate test' reveals you wouldn't choose what you currently have; when negotiation is stuck because the seller overvalues what they're giving up.

How it can help

When evaluating anything you currently own (assets, strategies, positions, employees): ask 'if I didn't already have this, would I acquire it at the current price?' If the answer is no, the endowment effect is inflating your valuation. In portfolio management: would you buy this stock today at its current price? If not, why are you holding it? In strategy: would you adopt this approach today if starting fresh? If not, you're endowed with a strategy you wouldn't choose. The 'clean slate' test: regularly evaluate your holdings, commitments, and positions as if you were acquiring them fresh.