strategy
Variance
Also: standard deviation, swings
The natural swing in results caused by luck in the short term. Even a winning player has losing months; variance is measured in buy-ins or big blinds per hundred hands and dictates how big a bankroll you need.
Example. After 20,000 hands a solid winner can still be below expectation — that is variance, not necessarily bad play.
In no-limit cash games a typical standard deviation is around 80–100 big blinds per 100 hands; in large-field tournaments variance is enormous because most of your profit comes from rare deep runs. Understanding variance keeps players from over-reacting to short samples and from playing stakes their bankroll cannot support.