Strategy
Common mistakes new prediction market traders make
Eight mistakes that cost beginners money — and how to avoid each. Most of these are obvious in hindsight, painful to learn the hard way.
Prediction markets reward discipline more than intelligence. Here are the eight mistakes that cost the most new traders the most money. Each is followed by what to do instead.
1. Betting on what you want to happen
The single most expensive mistake. Markets touching politics, sports, your favorite company — anywhere you have an emotional stake — are the worst markets for you to trade. You'll systematically overestimate the probability of your preferred outcome.
Fix: If you can't argue both sides of a market with equal energy, don't trade it. Period.
2. Sizing in proportion to confidence rather than bankroll
New traders bet $50 on things they're "kinda sure of" and $500 on things they're "really sure of". This is exactly backward. The really-sure-of trades are usually closer to consensus, where edge is small. The kinda-sure-of trades sometimes have larger edge.
Fix: Size all trades from a fixed framework like quarter Kelly, not from gut feel.
3. Ignoring resolution criteria
"Will Trump win the 2024 election?" sounds clear. The actual contract resolution rules specify which Electoral College count, which date, which official source, and what happens to the market if any of those are delayed. Skim the rules and you'll be the one writing "I should have won" posts.
Fix: Read the resolution rules of every market before placing your first trade in it. Five minutes of reading averts all-day complaints.
4. Trading thin markets at full size
A market with $2,000 of total volume can move 10 percentage points on one mid-sized bet. If that's you, you've just paid 10 cents per share more than you needed to. If someone else does it, your position can swing wildly without any actual news.
Fix: Check 24h volume before entering. For thin markets (under $50K daily volume), use limit orders only and size at one quarter or less of what Kelly suggests.
5. Chasing longshots for the payoff
A market trading at 5 cents pays $19 of profit per dollar risked if it hits. That feels like free money. It is not. The market priced it at 5% because it's a 5% event, and you'll lose 95% of those bets.
Fix: Only buy longshots when you have a specific reason the market is mispriced. "It would be cool if it happened" is not a reason. Read reading odds correctly.
6. Holding through resolution when the thesis already paid off
You bought at 40, the price moved to 75, and you're confident it'll resolve at 100. Holding to resolution makes sense, right? Not always. The current 75 is a bird in the hand. Holding for the extra 25 cents while risking that something weird happens at resolution is often a bad trade.
Fix: When a market reflects most of what you knew, take the gain. The opportunity cost of locked capital is real.
7. Doubling down on losses
You bought at 60 cents and now it's at 40 cents. You're more sure than ever. So you buy more.
Sometimes this is correct. Most times the market knows something you don't, and your averaging-down is just confirmation bias eating your bankroll. The price moved against you for a reason. Investigate the reason before adding to the position.
Fix: Adding to losing positions requires new information, not just unchanged conviction. If nothing has happened to refute the market's move, don't add.
8. Not tracking results
You can't tell if you have edge if you don't keep records. Most traders rely on memory, and memory is biased toward winning trades. Without a real log, you'll think you're up when you're flat or down.
Fix: Spreadsheet or notebook. For every trade record: market, your probability estimate, market price at entry, position size, your thesis. After 50 resolved trades you'll have honest data on whether you have edge.