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Glossary

Non-fiction concepts that recur across the library

66 canonical ideas you'll meet across the Read Stacks library — from System 1 thinking to the obstacle is the way. Each entry is source-cited, plain-English, and quotable in 1-2 sentences. Use this page as a fast-lookup index when reading any chapter summary.

Psychology + cognition

Sunk cost fallacy

The error of treating already-spent time, money, or effort as a reason to continue. Rational choice ignores sunk cost: what matters is whether the next dollar (or year) is the best use, not what you’ve already paid. Common in failed projects and relationships.

Cognitive bias

Also: Systematic error · Heuristic error

A systematic deviation from rational judgment caused by mental shortcuts (heuristics). The ~200 documented biases — confirmation bias, anchoring, loss aversion, sunk cost fallacy, availability heuristic — explain why intelligent people repeatedly make predictable mistakes in identifiable situations.

Hawthorne effect

Also: Observer effect

The phenomenon where people modify their behavior because they know they're being observed. Named after 1920s Hawthorne Works factory studies. The implication for behavior change: simple measurement often produces improvement before any actual intervention.

Survivorship bias

Drawing conclusions from a sample that only includes successes — because the failures aren't around to be counted. Why "all successful founders dropped out of college" lies: the failed dropouts aren't in the survey. Recognizing it changes how you read success literature.

Halo effect

Edward Thorndike's name for the cognitive bias where one positive trait colors our perception of unrelated traits. Attractive people are assumed smart; charismatic leaders are assumed competent. Drives hiring mistakes, brand premiums, and most "this CEO is a visionary" narratives.

Cognitive dissonance

Leon Festinger's 1957 framework: the discomfort of holding two conflicting beliefs simultaneously. Resolved by changing one belief, rationalizing, or avoiding contrary information. Drives most "I knew it all along" reconstructions + much of why facts rarely change minds.

Decision fatigue

The deterioration of decision quality after making many decisions in succession. Why judges grant parole more in the morning, why CEOs wear the same shirt daily, why grocery shopping at 8pm leads to junk food. Each decision spends a finite daily resource.

Habits + behavior change

Compound effect

The disproportionate long-term result of small, repeated actions. Money compounds; so do habits, relationships, skill, and reputation. The compound effect is invisible at week 4 and undeniable at year 4. The trap is judging early; the leverage is staying.

Persuasion + influence

Stoic philosophy

Mindset

Skill + career

Flow state

Mihaly Csikszentmihalyi’s name for the psychological state of complete absorption in an activity at the edge of skill. Time distorts, self-consciousness drops, performance peaks. Flow requires clear goals, immediate feedback, and challenge that slightly exceeds current ability.

Spaced repetition

A learning technique that reviews material at increasing intervals to maximize retention. Based on the Ebbinghaus forgetting curve (1885). Anki + SuperMemo + most flashcard apps implement it. The practice that makes summary-reading actually compound into memory.

Antifragility + risk

Business + strategy

Circle of competence

Warren Buffett (popularized by Naval + Ray Dalio): the set of domains where your knowledge is genuinely deep. Stay inside it for big bets. The danger isn’t having a small circle — it’s misjudging the size of your circle. Most expensive mistakes happen at the edges.

Pareto principle (80/20 rule)

Also: 80/20 rule · 80-20 rule

Vilfredo Pareto's observation that 80% of effects come from 20% of causes. 20% of customers produce 80% of revenue; 20% of features get 80% of use; 20% of habits drive 80% of results. The corollary: most effort is wasted on the trailing 80% that produces 20%.

Negotiation + communication

BATNA

Also: Best Alternative to a Negotiated Agreement

Roger Fisher and William Ury’s term from Getting to Yes: the best outcome you can secure without the current deal. Your BATNA is your leverage — the worse the alternative, the weaker your position. Strengthen BATNA before negotiating, not during.

Attention + focus

Why this exists. When you read non-fiction chapter summaries on Read Stacks, the same concepts keep recurring across books. Atomic Habits and Power of Habit both rely on the habit loop. Cialdini's Pre-Suasion builds on his own Influence. Newport's Deep Work extends Ericsson's deliberate practice. This glossary is the fast-lookup index — bookmark it, search it, link to it.

Want to suggest a concept to add? Email [email protected] — every reply is read by the operator personally.