Why did gamblers lose millions betting against 26 blacks in a row?

On August 18, 1913, the roulette wheel at the Monte Carlo Casino landed on black 26 times in a row. Gamblers, reasoning that the streak had to be followed by red, bet against black and lost millions of francs. The odds of landing on the same color 26 times in a row are genuinely tiny — about 1 in 68.4 million — but that streak didn't make the 27th spin any more likely to be red. Each spin of a fair wheel is completely independent of the last, so the probability of red stayed exactly what it always was.

Psychologists call this mistake the gambler's fallacy: believing an outcome that hasn't happened in a while is somehow "owed." Daniel Kahneman and Amos Tversky traced it to a mental shortcut called the representativeness heuristic — people judge how likely something is by how similar it seems to what they have seen before, and a long run of one colour doesn't look the way randomness is supposed to look. It isn't just theoretical: in an analysis of security-camera recordings from a Nevada casino, gamblers became more and more likely to bet against a streak the longer it ran.

Here's what makes casinos unbothered by any of this: the house edge. That's the built-in percentage of each bet the casino expects to keep over time, baked into the rules themselves rather than into any streak. On American roulette, with two zero pockets, it's 5.26%; on European roulette, with just one zero, it drops to 2.7%. Other games vary even more — keno can run a house edge as high as 25%, some slot machines up to 15%, while some games have an edge as low as 0.3%.

That edge doesn't care whether players believe in lucky or unlucky streaks — it applies to every single spin, independent of what came before. The one real exception is games where outcomes aren't independent, like blackjack: once cards are dealt and not reshuffled, the odds of drawing a particular card actually do shift, which is exactly what makes card counting work. But on a roulette wheel, there's no streak, hot or cold, that changes the math — only the house edge grinding on, spin after spin.