5 Psychological Biases Destroying Your Portfolio Returns

Behavioural finance has documented over 180 cognitive biases. But five dominate investor losses: loss aversion, recency bias, anchoring, the endowment effect, and FOMO. Academic research has now quantified exactly how much each one costs — and the numbers are larger than most investors realise.

1. Loss Aversion (Cost: ~2.4% annually)

Kahneman and Tversky's foundational research showed that losses feel approximately 2× more painful than equivalent gains feel pleasurable. The investing consequence: investors hold losers too long (hoping to break even) and sell winners too early (locking in the gain before it disappears). Odean (1998) showed this "disposition effect" reduces returns by approximately 2.4% per year on a risk-adjusted basis.

2. Recency Bias (Cost: ~3.1% annually)

We disproportionately weight recent experience when forecasting. After a market crash, investors underweight equities for years. After a bull market, they overweight them going into peaks. Dalbar's annual QAIB study shows the average equity investor underperforms the S&P 500 by 3.1% annually, almost entirely attributable to performance-chasing behaviour driven by recency bias.

Why Value Investing Is a Natural Antidote

The Graham methodology is explicitly designed to remove behavioural discretion from the process. When you buy by formula — NCAV discount, insider signals, Score threshold — you buy what's cheap and hated, not what's popular and exciting. You sell by rule when the discount closes. The system forces you to do the opposite of what feels right, which is precisely why it works.