"The YES price is already 0.9. Isn't this an obvious sure win?" I have seen quite a few people rush in with this idea, only to be confused about why they lost money at settlement. In fact, 0.9 dollars is not a "sure win price" at all. It only means one thing: the market thinks there is a 90% chance this event will happen, not that it has already happened.
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The Core Issue: Probability Is Not Certainty, and Price Is Not a Guarantee
This may sound like wordplay, but there are two completely different concepts behind it:
Probability: 0.9 means the market thinks there is a 90% chance the event will happen.
Price: 0.9 dollars is the cost of buying one YES share.
If the event actually happens, your YES share becomes 1 dollar, so you earn 0.1 dollars per share, or a 10% return. If the event does not happen, your YES share becomes 0, so you lose 0.9 dollars per share, a 100% loss.
You may think 0.9 is very safe, but its profit-to-loss ratio is 1:9. You win 10% when you are right, but you lose 90% when you are wrong. That is the real meaning of "high probability."
YES + NO = 1 Does Not Mean "One Will Win and One Will Lose"
In every binary market on Polymarket, the prices of YES and NO always add up to about 1 dollar. This mechanism exists because:
You spend 1 USDC to mint one "complete set" of one YES share and one NO share.
At settlement, only the winning side is worth 1 dollar, and the losing side goes to zero.
So the saying "price equals probability" is an equivalent expression. A YES price of 0.7 dollars means the market thinks there is a 70% chance the event will happen, while a NO price of 0.3 dollars means a 30% chance it will not happen. The two always add up to 100%.
But there is an easily overlooked detail here: probability is produced by market trading, not by objective fact. The market can be collectively wrong. During the 2024 US election, some Polymarket market prices clearly deviated from the final results. That is not a platform problem, but a problem of participants making inaccurate judgments.
So Why Can't You Just Trust a "0.9 Price"?
Treating 0.9 as a "sure win" and betting on it will cause you to stumble in two places:
1. The real risk in high-probability markets is underestimated
A YES price of 0.9 means your profit space is only 10% (1 - 0.9 = 0.1). But if that 10% low-probability event happens, you lose 90% of your principal. You are using a 1:9 profit-to-loss ratio to bet on a situation with a 90% win rate. Over the long run, the expected value is roughly flat, not a guaranteed profit.
2. Prices are affected by liquidity and large orders, not by pure "probability"
In markets with poor liquidity, one small trade can push the YES price from 0.5 to 0.8. That price reflects "someone spent a lot of money," not "a collective judgment based on sufficient information." When liquidity is insufficient, there can be a large gap between price and true probability.
Risk warning: If unfavorable news appears before expiration, a YES price of 0.9 can instantly drop to 0.3. The moment you think it is a "sure win" is exactly the moment when you are taking the most risk and have the least room for error. In prediction markets, there is no such thing as a "sure win." There is only a trade-off between "a high chance of winning but earning little" and "a low chance of winning but earning a lot."
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Before Placing an Order, Think Clearly About These Three Points
Is this price a probability or a guarantee? It is a probability, not a guarantee. A 90% win rate means there is a 10% chance you will lose everything.
Is there enough liquidity in this market? In markets with wide bid-ask spreads and thin trading, prices can easily become distorted. Do not treat them as true probabilities.
Are you buying probability, or are you gambling on certainty? If you bought at 0.9 because you "felt it was a sure win," it is worth recalculating the profit-to-loss ratio.
