Decision point · Aug 2012
Buffett & Tesco — the "huge mistake"
Buffett later called the Tesco position "a huge mistake." Quality-trap warning lights were already on.
Berkshire built a 5%+ stake in UK supermarket leader Tesco from 2006–2012, attracted to its dominant market share, ROE history, and apparent moat in retail logistics. The thesis was classic Buffett: "great brands at fair prices."
“Buffett later called the Tesco position "a huge mistake." Quality-trap warning lights were already on.”
A 2014 accounting scandal revealed £263M of overstated profits. Margins collapsed under pressure from German discounters Aldi and Lidl. Berkshire eventually sold at a roughly $444M after-tax loss, and Buffett wrote in the 2014 letter that he had not "been quick enough."
A Prism memo at the 2012 decision point would have flagged growth_deceleration on consecutive quarters of margin compression and a quality-trap pattern on the rising leverage + falling ROIC combination. The disagreement classifier would have surfaced a quality-vs-valuation debate with Marks and Greenblatt rejecting the setup.
Patterns the engine would have flagged
- accounting_red_flag
- growth_deceleration
Negative signals at the time
- Quality (margin compression)
- Event (deteriorating earnings cadence)
“The moat narrative is what gets you in.”
The same multi-framework engine running on every memo today would have surfaced this as a majority-bearish disagreement at the decision point, not in retrospect.
Howard Marks
Marks (Risk-aware value)
Margin compression in a structurally-pressured industry is a sentiment trap, not value.
Joel Greenblatt
Magic Formula
Falling ROC + falling earnings yield disqualifies — the formula explicitly avoids deteriorating fundamentals.
The moat narrative is what gets you in. The quality-trap pattern (rising leverage + falling returns) is what should get you out. Buffett's own retrospective frames it the same way — he was slow to act on the margin signal.
Primary sources
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