A Polymarket whale loses a year of gains on one bet

Trading near-certainties on prediction markets looks safe until one loss wipes out hundreds of your wins. TheMonaLisaCode, a wallet our alert system recently flagged, is a perfect example.

On September 17, the wallet paid $110,955.88 for Bills contracts at 99.9 cents on Polymarket's Lions vs. Bills market at 11:11 PM ET. The price had jumped from 97.75 to 99.45 cents a minute or two earlier. The Bills won 41-31, and 37 minutes after buying, the wallet collected $105.51 in profit. Each contract pays $1 if the Bills win, so the buyer risked 99.9 cents to make a tenth of a cent. Over many bets, this only works if the buyer is wrong less than once in 1,000 tries. The wallet had about $1,052 at risk for every $1 it made.

Since May 2, TheMonaLisaCode has bought $3.75 million of contracts, 91% of it at 99.5 cents or more, at an average of 99.47 cents. At that price, it earns at best 53 cents per $100 and can afford to lose only about $1 in $189. Counted by event, the strategy seems to work, as 90 of 92 trades made money, one broke even, and one lost.

That single loss came on the Iran airspace market, which, according to the rules, paid 'Yes' on a broad shutdown of commercial flights across Iran or a major region of it, but not on partial closures. On May 23, Tehran time, Iran suspended civil flights in its west, with only eight airports open nationwide. Between 1:55 and 4:38 AM ET that day, with the May 27 'Yes' near 99 cents, the wallet bought 'Yes' on four deadlines at 95 to 99 cents. Unfortunately, by 5 AM, that contract was at 56.65 cents. The wallet sold everything from 5:07 PM at 16 to 40 cents, and both May contracts settled 'No'.

That bet represented just 0.6% of its total buying. However, its $16,914.07 loss equals the profit on 160 trades like the Bills one and erased 89% of what its 90 winners made. The profile shows about $2,200 of total profit now. One miss turned a year of grinding into barely breaking even.

The math behind this approach is just broken. When you buy at 99 cents, you are saying the event is almost certain to happen. But markets price in consensus belief, not objective truth, and black swan events happen more often than you expect. A single 50-cent move against you, which occurs whenever unexpected news hits, destroys the profit from 50 successful trades.

This strategy also creates a psychological trap. A string of 90 wins creates false confidence, making you size up just before the one loss that matters. Human brains are wired to extrapolate recent success, but prediction markets are not slot machines with fixed odds. Every trade carries unique tail risk, and near-certain contracts hide the most dangerous exposure because they attract the most complacency. We think near-certainties offer the worst risk-reward in prediction markets, and the only way to win is to avoid them entirely.