We’ve all been there: you’re at a pick-up roleplaying group at your local game shop, and that noisy munchkin to your right—who is playing some kind of half-dragon triple-multiclassed character from an out-of-print rulebook that he found a PDF of online—seems to roll more than his fair share of natural 20s. Okay, maybe we haven’t all been there, but let me tell you: it’s annoying when someone appears to be awfully lucky with their rolls.

The issue is slightly less pronounced with board games, where everyone tends to use the same pool of dice, but having dice regularly come up high or low can obviously affect how the game plays out.

Putting aside cases of intentional cheating, did you know that dice—particularly polyhedral dice like d20 or d8—are almost universally unbalanced? Some are more balanced than others, but as you’d expect from mass-produced objects, small flaws in manufacturing and materials nearly always push each individual die either above or below the expected average roll.