#1
Betting size instead of edge
Position size should follow the gap between your estimate and the price, not how confident you feel. Run it through Kelly and cut the result.
9 mistakes that drain beginner accounts
Short answer
Most prediction-market losses are not forecasting failures — they are sizing, spread and resolution failures. Fix those three and an average forecaster stops bleeding.
#2
Buying longshots because they pay 10×
A 10¢ contract needs a 10% hit rate. The favourite-longshot bias exists because that rate is almost always lower than it looks.
#3
Ignoring resolution wording
You can be right about the world and lose on a technicality. Read the source, the deadline and the ambiguity clause before entering.
#4
Trading the mid, filling at the ask
Your EV must be computed at the price you actually get. On thin markets the spread eats small edges whole.
#5
Overtrading five-minute binaries
Round-trip costs apply per trade. Twenty trades a day at 1% friction is a 20% daily drag on a stake's worth of capital.
#6
Copying whales blindly
Leaderboards rank by profit, which one lucky bet can produce. Copy hit rate within a category, not headline P&L.
#7
Averaging into a losing thesis
Adding is only correct when the price moved and your estimate did not. If the news changed your estimate, adding is denial with extra steps.
#8
No trade log
Without recorded probability estimates you can never tell whether you are calibrated. Fifty logged trades is the minimum honest sample.
#9
Treating a terminal as an edge
Better tooling removes friction and shows you flow. It does not supply a view. The view is still your job.
FAQ
+ What is the single most expensive beginner mistake?
Position sizing. Traders with a genuine edge still blow up by betting far past Kelly, because variance on binary contracts is brutal over short samples.
+ How do I avoid the longshot trap?
Before buying anything under 20¢, write down the hit rate it requires and ask whether your history supports it. Most people's does not.
+ Should beginners use a terminal at all?
Yes, but for discipline rather than speed: seeing exposure, spread and flow in one place prevents most of the errors on this list.
Fix the biggest one first: size your next position properly.