Mental accounting, a concept introduced by Richard Thaler, describes how people categorize, evaluate, and track financial activities in separate mental accounts rather than treating money as fully fungible. A consumer might refuse to spend $50 from a "savings" account on dinner but happily spend a $50 gift card on the same meal, even though both have identical monetary value. Mental accounting also gives rise to the house money effect, where people take greater risks with money perceived as winnings — such as casino profits — because it is mentally categorized as "free money" rather than part of personal wealth. Similarly, people continue investing in failing projects because they have a mental account tracking prior expenditures and feel compelled to justify sunk costs, an instance of the sunk cost fallacy that distorts business decisions when executives fund losing ventures to defend past spending.
Framing effects reveal that decisions depend not only on objective facts but also on how information is presented. In Kahneman and Tversky's Asian Disease Problem, participants preferred a sure option when outcomes were framed as lives saved but switched to the risky option when framed as lives lost, even though the underlying probabilities were identical. The isolation effect, or cancellation effect, compounds this: people tend to disregard components shared by all options and focus only on what differs, leading to preferences that depend on how the choice is described. Narrow framing and narrow bracketing describe related problems in which each financial decision is evaluated in isolation rather than as part of a broader portfolio, producing choices that are locally sensible but globally suboptimal. Mental accounting's payment depreciation concept captures how the psychological pain of paying diminishes over time, which is why prepaid vacations feel "free" and why consumers often prefer flat-rate pricing.
The endowment effect, demonstrated experimentally by Kahneman, Knetsch, and Thaler in their classic mug-trading studies, shows that people value an object more highly simply because they own it. Sellers typically demand roughly two to three times the price that buyers are willing to pay for the same object, creating a substantial gap between willingness to accept and willingness to pay. Prospect theory explains this asymmetry by treating giving up a good as a loss relative to the ownership reference point, which feels more painful than the buyer's anticipated gain. The effect influences real estate markets, where homeowners set asking prices anchored to their purchase price and refuse to sell at a loss even when market conditions have changed. Investors exhibit analogous behavior, demanding a higher price to sell a stock they own than they would pay to buy the same stock, contributing to market inefficiencies. Status quo bias operates through a similar mechanism: any change from the current state involves potential losses in some dimension, and because losses loom larger than gains, people disproportionately favor staying put.