The sunk cost fallacy occurs when traders continue holding a losing position or investing additional capital because of the resources already committed, rather than evaluating the position on its current merits and future prospects. The time, money, and emotional energy already spent become anchors that prevent rational decision-making, leading to escalating commitment to failing trades.
Sunk costs are past expenditures that cannot be recovered regardless of future actions. Rational decision-making should only consider future costs and benefits, not past commitments. Traders fall into this trap by averaging down into losing trades without new analytical justification. Emotional investment in a trade thesis makes abandoning it feel like admitting failure. The fallacy is amplified when the trader has publicly shared their position or analysis. Opportunity cost: capital locked in a losing trade cannot be deployed in better opportunities.
Before averaging down, ask whether you would enter this trade fresh at the current price with no existing position. Treat every moment as a new decision: is the expected value of holding positive from this point forward? Set a maximum number of additions to a position and a maximum total allocation before the trade begins. Document the specific conditions that would invalidate your thesis before entering.
Exit when the original thesis is invalidated, regardless of accumulated losses. Close positions where the only reason for holding is the amount already lost. Review positions weekly and ask: if this were cash, would I choose to invest it here today? Set a maximum drawdown per position that triggers automatic closure.
Ongoing — applied to every position review and evaluated weekly
The most effective defence against the sunk cost fallacy is reframing every position as a new decision each day. Ask yourself: given everything I know now, would I enter this trade today at this price? If the answer is no, the rational action is to close the position immediately, regardless of past losses. The past investment is irrelevant to the future expectation.
The overconfidence effect causes traders to overestimate their knowledge, skill, and ability to predict market outcomes. After a winning streak, traders often increase position sizes, ignore their rules, and take trades that don't meet their criteria — believing they have a 'hot hand'. Overconfidence typically precedes the largest drawdowns in a trader's career.
Hindsight bias is the tendency to believe, after an event has occurred, that you predicted or expected the outcome all along. In trading, this manifests as reviewing charts after the fact and feeling certain that the signals were obvious, leading to overconfidence in future predictions and an underestimation of real-time uncertainty. This bias distorts trade journaling and prevents genuine learning from both wins and losses.
Mental accounting is the cognitive bias of treating money differently based on its source, intended use, or the mental 'account' it is assigned to — even though all money is fungible. In trading, this manifests as treating profits differently from initial capital (risking 'house money' more freely), segregating portfolio performance by position rather than total, or taking excessive risk with bonus or windfall funds.
Revenge trading is the emotionally driven behaviour of immediately re-entering the market after a loss with the goal of recovering the lost money as quickly as possible. This reactive pattern abandons the trading plan, increases position sizes, and lowers entry standards — compounding losses rather than recovering them. Revenge trading is one of the most destructive behavioural patterns and is responsible for turning manageable losses into account-threatening drawdowns.