Pseudo-random distribution
Also said as PRD, Bad luck protection, Shuffle bag
Randomness that bends towards its average: each miss raises the chance of the next hit, and each hit resets it. The long-run rate stays the same and the streaks mostly go away. A shuffle bag does a similar job by dealing out a fixed set.
True randomness is streaky, and people read streaks as broken. A 25% crit that fails twenty times looks like a bug, and it will happen to somebody. PRD removes those stories, along with the lucky streaks.
Say it
“Use a pseudo-random distribution on crits: 25% overall, but start at 8.5% and add 8.5% per miss, so that nobody can ever miss twelve in a row.”
Where you’ve seen it
Dota 2 uses it for many chance-based effects. A 25% chance starts at about 8.5% and adds that much again after every miss, until it fires and starts over.
Not to be confused with true random
With true random each roll ignores the last, so a 25% chance is always 25%. With PRD, a miss makes the next roll more likely. Over thousands of rolls both give about 25%.