Losses Hurt Twice as Much — Kahneman & Tversky

The finding

Prospect theory (Kahneman & Tversky, 1979): the pain of a loss is roughly TWICE the pleasure of an equivalent gain, and people evaluate outcomes as gains/losses from a REFERENCE POINT (usually purchase price), not from total wealth. This single asymmetry explains most trading pathologies: cutting winners early (lock the pleasure), riding losers (avoid realizing the pain).

The disposition effect

The measured result: investors sell winners ~1.5× faster than losers. Selling winners feels good and feels safe; selling losers admits error and realizes pain. The irony is total: the winner sold early was doing its job (the edge), and the loser held "until it comes back" is usually a thesis already dead. Taxes add insult: winners trigger gains, losers could harvest losses.

The structural fix

Same as every bias: pre-commitment. Exits defined at ENTRY (stop = 1R, target/trail plan), position review on THESIS not price ("is the reason I bought still true?"), and a journal that records what the pre-trade self decided so the in-trade self cannot quietly renegotiate. You cannot feel your way past loss aversion; you can only build around it.

Sources

• Prospect Theory (1979)Kahneman & Tversky
• Disposition EffectInvestopedia