Selling & Mistakes

Learning objectives

By the end you can:

1. Explain why selling is structurally harder than buying: you own the asset (endowment, loss aversion, sunk cost, and the disposition effect all now bind), the cost basis contaminates the decision as an anchor, and the sell decision is chronically under-instrumented because almost everyone journals buys and no one journals sells.
2. State and apply the five legitimate reasons to sell, each with its one-question decision test: (1) the thesis is broken; (2) you recognized a mistake; (3) the price is far above intrinsic value; (4) a materially better opportunity exists; (5) the position has grown beyond your risk tolerance. Then correctly classify which two are tax-blind (non-negotiable) and which three are tax-modulated (discretionary).
3. Distinguish a broken thesis from a fallen price using the written thesis in your decision journal as the arbiter, separating a load-bearing pillar actually breaking from thesis-noise (a weak quarter) or a thesis merely playing out slowly. Distinguish too a mistake (wrong at purchase) from bad luck (right process, bad outcome).
4. Compute the cost of selling a compounder too early, the 3× versus 100× arithmetic, and explain why "no one ever went broke taking a profit" is one of the most expensive clichés in investing, using the positive skew of equity returns (Bessembinder) and Munger's first rule of compounding.
5. Diagnose the disposition effect operationally through Freeman-Shor's five tribes (The Art of Execution): Rabbits and Raiders as the losing archetypes, Assassins, Hunters, and Connoisseurs as the winning ones. Explain why execution after the buy, not hit rate, separated his elite managers.
6. Pre-commit sell criteria at the moment of purchase, writing the thesis-break triggers, the overvaluation zone, and the maximum-size/trim rule into the buy note before you own the position. Argue the case for thesis-based versus mechanical price-stop selling for a fundamental investor.
7. Run a tax-aware sell decision across India (LTCG/STCG, the 12-month line) and the US (long- versus short-term, the 1-year line), computing the after-tax hurdle a switch must clear and explaining deferred tax as an interest-free loan that rewards patience.
8. Build and use a mistake taxonomy (commission versus omission; analytical versus behavioral versus bad-luck) and feed each learnable mistake through the M6.05 root-cause loop into a permanent checklist line, while correctly refusing to "learn" from genuine bad luck.

Prerequisites & connections

Builds on. M6.04 (Behavioral Finance) is the indispensable prerequisite: the disposition effect (riding losers, cutting winners), the fresh-money test ("ignoring what I paid, would I buy this at today's price?"), and the biases that bind hardest at the sell decision (anchoring to cost, loss aversion, sunk cost, endowment) are all taught there and operationalized here. This module is §4.8 of M6.04 (the behavioral edge) turned into a specific exit discipline. M6.05 (Checklist & Temperament) gives you the decision journal and the mistake-to-checklist loop; the journal is the arbiter of the "is the thesis broken?" question, and the mistake taxonomy you build here is the sorting stage that feeds that loop. M6.03 (Mental Models) supplies opportunity cost / hurdle rates (sell reason 4), process-over-outcome (the mistake-versus-bad-luck distinction), and inversion. M9.01 (Risk & Position Sizing) defines risk as probability × magnitude of impairment and gives the sizing discipline behind sell reason 5 (trim to your cap). M9.02 (Portfolio Construction) supplies your written concentration policy (the maximum single-position weight that reason 5 enforces) and the opportunity-cost hurdle that reason 4 tests against. M3 (Valuation) is the machinery for reason 3: intrinsic value, margin of safety, and the reverse DCF (M3.05) that reads what a price implies. M6.01/M6.02 supply the philosophical spine: Graham's margin of safety (whose reverse is the margin of danger), Fisher's three reasons to sell, Terry Smith's "do nothing," and the quality-compounder school that makes running winners rational.

Feeds forward. M9.04 (The Process + Phase Capstone) folds selling into the single running loop of checklist → journal → quarterly review → calibration, and requires a simulator season in which your sells are journaled and scored, not just your buys; this module authors the sell station of that process. Phase 10 (the two capstone deep dives, M10.01–M10.02): every institutional-grade thesis you write there must end with an explicit sell-criteria section (business, why it is a good business, the variant perception, valuation and expected return, and the pre-registered sell triggers), exactly the artifact §4.10 teaches you to write. The decision journal and calibration threads that run to the end of the program are fed here by the discipline of recording every sell reason and later scoring it. Competency C9 in the master map, "an investor's temperament and process", is substantially certified by this module and completed in M9.04.