The Disposition Effect, identified by Shefrin & Statman (1985), is the documented tendency of investors to sell winners too early and hold losers too long. It is a direct consequence of loss aversion combined with mental accounting at the position level.
Plain-English example
An investor's portfolio has BAJFINANCE up 40% and VODAFONE-IDEA down 60%. She sells BAJFINANCE to "book profits" (locking in tax + losing future compounding), and holds VI because "selling means accepting the loss". A year later BAJFINANCE is up another 25%, VI is down a further 40%. Classic disposition-effect destruction of compounding.
Why it happens
- Booking gains delivers the dopamine hit of "being right"
- Selling losers forces the painful admission of being wrong
- Tax bias in some jurisdictions (less so in India where harvest losses is actually beneficial)
- Mental accounting at the stock level instead of portfolio level
How to mitigate
Pre-commit to thesis-based selling, not price-based. Document buy thesis; sell when thesis breaks, not when price moves. Harvest tax losses systematically (Indian STCG/LTCG offset rules). Use trailing stops on momentum positions; rebalance to target weights mechanically.
SEBI caveat
The bias persists even among professionals. Tax-loss harvesting in India follows specific STCG/LTCG set-off rules — confirm with a CA. Education only.
Related
See also Loss Aversion, Anchoring, Mental Accounting.