Ch1. Introduction to Behavioral Economics — Why Humans Make Irrational Decisions

Why Do Humans Make Irrational Decisions?

Traditional economics assumes that humans are Homo Economicus — rational agents who possess complete information and act to maximize their own utility.

Reality tells a different story.

People:

Feel that a product must be a better deal when it’s marked down from a high original price (anchoring)
Experience the pain of losing $100 as more than twice as intense as the pleasure of gaining$ 100 (loss aversion)
Choose $50 today over$ 100 in three years, yet also choose $5 tomorrow over$ 10 today (present bias)

The discipline that studies these inconsistencies is Behavioral Economics.

The Birth of Behavioral Economics

Behavioral economics emerged in the 1970s from the collaboration of two psychologists.

Daniel Kahneman and Amos Tversky began documenting decision-making patterns that classical economics could not explain. Their research culminated in the 1979 landmark paper Prospect Theory, and Kahneman was awarded the Nobel Prize in Economics in 2002 (Tversky had passed away in 1996 and was ineligible).

Richard Thaler extended the field — introducing mental accounting and the nudge framework — and received the Nobel Prize in Economics in 2017.

Core Concept 1: Prospect Theory

The central insight of Prospect Theory is that people respond not to outcomes in absolute terms, but to changes relative to a reference point.

Three Properties of the Value Function

Reference Dependence: People evaluate outcomes as gains or losses from their current state — not as absolute levels of wealth.
Loss Aversion: Losses hurt approximately 2.25 times more than equivalent gains feel good. “Losing $1,000" is far more painful than "gaining$ 1,000” is pleasurable.
Diminishing Sensitivity: The marginal impact of gains and losses decreases as they grow larger. Going from $100 to$ 200 feels better than going from $1,000 to$ 1,100, even though both are $100 gains.

Real-Life Applications

Stock investing: Loss aversion makes investors hold losing positions too long. “If I sell now, I lock in the loss.”
Insurance: Actuarially the premium may exceed expected loss, but the fear of losing assets drives people to buy coverage.
Return policies: “30-day money-back guarantee” leverages loss aversion — consumers feel safer because potential loss is reduced.

Core Concept 2: The Anchoring Effect

Anchoring is the cognitive bias by which the first number or piece of information encountered has a disproportionate influence on subsequent judgments.

Kahneman and Tversky’s Experiment

Participants watched a roulette wheel stop at either 10 or 65 (the outcomes were rigged), then were asked: “What percentage of UN member states are African countries?”

Group that saw 10: estimated an average of 25%
Group that saw 65: estimated an average of 45%

A completely random, irrelevant number produced dramatically different judgments.

Real-Life Applications

Negotiation: The party who names a number first sets the anchor. High first offers yield higher final settlements.
Price tags: “Original price $200 → Sale price$ 120” establishes $200 as an anchor, making$ 120 feel like a bargain.
Salary negotiation: Candidates who state a (high) number first tend to receive higher offers.

Core Concept 3: Mental Accounting

Richard Thaler’s concept: people sort money into separate psychological accounts based on its source and intended use, then apply different rules to each account.

Examples

Winnings from gambling: spent freely (“found money”)
Earned wages: spent carefully

Logically both are identical dollars, but psychologically they are treated differently.

An unexpected bonus goes toward “home renovations”
The same amount received as salary gets saved

Real-Life Applications

Budget categories: People resist moving unspent “dining” budget into a “shopping” account
Credit cards vs. cash: Credit cards mute the “pain of paying,” leading to higher spending
Tax refunds: Treated as a windfall bonus, refunds disproportionately fund impulse purchases

Core Concept 4: Status Quo Bias

People have a strong tendency to prefer the current state over any change — largely because change implies the possibility of loss.

Experimental Evidence

1990s US auto insurance reform in New Jersey and Pennsylvania:

New Jersey: cheaper insurance (limited lawsuit rights) set as default → 80% chose it
Pennsylvania: more expensive insurance (full lawsuit rights) set as default → 70% chose it

The options were identical; only the default differed — yet the outcomes diverged by tens of percentage points.

Real-Life Applications

Auto-enrollment in retirement plans: Switching from opt-in to opt-out dramatically raises 401(k) participation rates
Organ donation: Countries with opt-out systems have far higher donation rates than opt-in countries
Subscription services: “Free trial — cancel anytime” exploits status quo bias; most people never cancel

Behavioral Economics Meets Policy: The Nudge

Thaler and Cass Sunstein proposed Nudge Theory — using cognitive biases to guide people toward better choices without coercion or mandates.

A nudge redesigns the choice environment so that better options become the path of least resistance.

Global examples:

UK Behavioural Insights Team: adding “9 out of 10 people in your area have already paid their taxes” to late-payment notices → 15% improvement in collection rates
Cafeteria placement: positioning healthy food at eye level → 25% increase in healthy choices
Fly sticker in urinals (Amsterdam airport): 80% reduction in restroom cleaning costs

Chapter Summary

Concept	Description	Real-Life Example
Prospect Theory	Losses feel ~2× worse than equivalent gains	Why investors hold losing stocks
Anchoring	The first number warps all subsequent judgment	Markdown pricing
Mental Accounting	Same money spent differently based on source	Spending windfalls vs. wages
Status Quo Bias	Preference for the current state over change	The power of default settings
Nudge	Better choices through environment design	Public policy applications

Next chapter: Present Bias and the Neuroscience of Procrastination — why your future self always seems like a better decision-maker, and how this shapes financial choices.

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