Variance is why you can make good bets and still lose money. It's why you can go 12-18 in a month despite being a long-term winner. And it's why bankroll management exists—to keep you alive long enough for your edge to overcome the random swings.
Understanding variance changes how you react to results. A bad week doesn't mean your process is broken. A hot week doesn't mean you're suddenly a betting genius. It's all noise until you hit a few hundred bets.
Variance is the statistical measure of how much your results will deviate from expected outcomes in the short term. Even a 60% winner will have stretches where they go 3-7 over 10 bets. That's not bad luck. That's variance.
The math is simple: if you're a 55% winner, you're also a 45% loser. Over 100 bets, you'll win about 55 and lose about 45. But over 10 bets? You might win 3 and lose 7. Or win 8 and lose 2. Both are well within normal variance.
You can't judge your betting skill based on 20 bets. You can barely judge it based on 100 bets. Even a 60% handicapper—which is elite—will have months where they dip to 52% purely due to variance.
This is why tracking long-term results matters. If you're hitting 54% over 500 bets, you're profitable. If you hit 48% over your last 50 bets, that doesn't mean you suddenly lost your edge. It means variance happened.
Professional bettors don't panic after a bad month. They trust their process over thousands of bets, not dozens. If your edge is real, it will show up in the long run. If it's not, no amount of short-term variance will save you.
Some bets have higher variance than others. Betting heavy favorites at -300 has low variance—you win often but for small amounts. Betting underdogs at +200 has high variance—you lose often but win big when you hit.
Neither is inherently better, but higher variance requires a bigger bankroll to survive the swings. If you're betting a lot of plus-money underdogs, you need more cushion to handle the losing streaks that will inevitably happen.
You can't eliminate variance. But you can control how much it affects you by managing your unit size.
Betting 1-2% per game means variance won't destroy you even during brutal losing streaks. Betting 10% per game means one week of bad variance can wipe out months of profit.
Variance is why Kelly Criterion and proper bankroll management exist. The math assumes variance will happen and protects you from going broke when it does.