The Madness of Markets: Alex Edmans on Why Smart Investors Make Crazy Decisions

“When people trade, even before fees and commissions, the average trade loses money.” — Alex Edmans

Isaac Newton might be able to foresee the movement of the stars, but he couldn’t foretell the madness of men. It was a lesson that cost the great physicist £4 million (in today’s money) when he threw his fortune into the South Sea Bubble. This priceless parable in Newtonian psychology opens The Madness of Markets, the new book by Alex Edmans — London Business School finance prof, old friend of the show, and author of the bestselling May Contain Lies.

Dr Edmans’s prognosis is bracingly unflattering to guys like Isaac Newton and Mark Twain who splurge their fortunes on speculative ventures. Intelligence, he reminds us, is domain-specific, but many smart people simply aren’t intelligent enough to realize this. So, in the age of Robinhood — when we can all trade anything from stocks, options, crypto to NFTs — the supposed wisdom of crowds is sometimes driven over the cliff by the irrational exuberance of dumb individuals.

Speaking of driving off the cliff, ninety percent of us think we’re above-average drivers, Edmans jokes, and this same delusion applies to markets. Unfortunately, such stupidity can be expensive for big brain types like Newton or Twain. “When people trade, even before fees and commissions, the average trade loses money,” he warns.

So close your Robinhood account and stick your cash in the bank? No, not quite. Know your edge, Edmans reminds us. And when it comes to making sense of the current AI boom, Edmans offers some particularly wise words. The AI sector trades at 25 to 30 times earnings rather than Cisco’s bubble-era 190, he notes, so it’s unlikely anyone will lose their life’s savings on Anthropic or OpenAI.

That said, the good doctor Edmans advises, don’t confuse your self-worth with your net worth. That’s a rookie conceit that only somebody as smart as Isaac Newton would fall for.

Five Takeaways

• Newton’s £4 Million. The book leads with the smartest victim on record: Isaac Newton rode the South Sea Bubble, banked a tidy profit, dove back in at the very top, and lost £20,000 — £4 million today — lamenting that he could predict the movement of the stars but not the madness of men. (Andrew’s companion case, via last month’s Citizen Twain episode with Jeff Jarvis: Mark Twain, genius writer, ruinous investor.) The lesson is that smartness is domain-specific: beating the market requires knowing the company, the industry, and — crucially — what’s already priced in. A great secretary of state evaluating Theranos is the Dunning-Kruger effect in a suit: expertise misapplied, one piece of the mosaic mistaken for the whole. Even Warren Buffett’s edge, Edmans notes, is partly restraint — don’t watch the market too closely, or you’ll mistake noise for signal.

• Know Your Edge. Edmans’s framework: play the market only if you can name your edge — knowledge (unique insight into a sector) or endurance (capital that can’t be withdrawn by flighty clients). His endurance exemplar is Clare College, Cambridge, which borrowed £10 million in the depths of 2008 and put it all into equities via its “2048 Fund”: a decade later the portfolio had tripled while the loan had merely doubled. No edge? Then “be humble” and hold a low-cost, globally diversified index fund — because the alternative is expensive. In the age of Robinhood, the market for everything has been democratized; the zero-commission promise is a myth (retail options bid-ask spreads run 20 to 25 percent); and the brokerage data is brutal: the average retail trade loses money before fees. “I’m generally a libertarian,” Edmans concedes — but decisions that jeopardize your financial future deserve a warning label.

• Why the Ox Doesn’t Apply. The week’s second Surowiecki appearance (after the Brunton episode): Edmans explains why the wisdom of crowds — the county-fair ox whose weight the crowd guesses perfectly — fails in markets. Two reasons: nobody is emotionally attached to the weight of an ox, and the guesses are secret. Stocks invert both — in a bubble everyone bids high together, and trading is public: Reddit threads, boasting friends, influencers, and the survivorship bias of gamblers who only mention their wins. Hence Andrew’s cocktail-party indicator, confirmed: when smart, successful people start telling you how much AI they’re buying, the trade is crowded and richly priced. The contrarian lineage — Graham, Buffett, Greenblatt — exists precisely to take the other side of mimicry. Or, per Andrew’s accepted inversion of the subtitle: why crazy investors make smart decisions — Ford’s faster horses, Moneyball’s walks, Jobs’s refusal to ask customers what they want.

• Is AI a Bubble? Maybe Not. The hour’s most contrarian calm. There are moments, Edmans says, when reasonable people could call a bubble in real time — Cisco in 2000 traded at a price-earnings ratio of 190, triple Microsoft’s. AI today trades at roughly 25 to 30 times earnings; the bear case is that those earnings rest on capex (Meta’s own investors say it’s spending too much) that may not be sustainable. His verdict: fairly priced, or modestly overvalued — “something about which reasonable people have different views.” On using AI to invest, the rule is anti-confirmation: don’t ask it why you’re right or to advocate for your pitch; ask it why you’re wrong, and let it gather mosaic pieces (Glassdoor culture scrapes) while humans still walk shop floors and read management’s eyes. Andrew’s gloss: it’s unlikely anyone will lose their life’s savings on Anthropic or OpenAI. The teaser: FT journalist Robin Wigglesworth — who blurbs this book “a maddeningly good read” and warns in the Times of the AI debt binge — visits this show soon.

• Cutting Our Flowers, Watering Our Weeds. Andrew’s Claudeception question — what happens when Anthropic feeds The Madness of Markets into its AI and everyone turns contrarian? — got a data answer: when a trading strategy is published in the Journal of Finance, its returns fall by only about a third. Money stays on the table because psychology is stubborn: momentum (buy six-month winners) has worked since 1993, yet it fights the disposition effect — our temptation to bank winners and cling to losers, chasing casino losses, “cutting our flowers and watering our weeds.” Timing cuts both ways: six-month winners keep winning, three-year winners revert — the foundation of contrarianism — but calling the market’s top or bottom is near-impossible, which is why Edmans bought heavily in late 2008 content to be “80 percent right.” And the closing wisdom, after Joe Kennedy’s 1928 exit and Trump’s well-timed memecoin: your self-worth should have nothing to do with your net worth — a rookie conceit, as Andrew’s intro has it, that only somebody as smart as Isaac Newton would fall for.

About the Guest

Alex Edmans is Professor of Finance at London Business School and a leading expert on market psychology. His research has featured in the Financial Times, The Wall Street Journal, and on the BBC, and he has advised sovereign wealth funds, pension funds, and asset managers worldwide. He is the author of May Contain Lies, an Amazon number-one bestseller disc...