The "1% rule" in bankroll management refers to the guideline that a player should never wager more than 1% of their total bankroll on a single bet or session. This approach helps minimize the risk of significant losses and allows players to endure the natural fluctuations of gambling without depleting their funds too quickly. By adhering to this rule, players can maintain a sustainable gambling practice, protecting their bankroll over the long term and allowing for continued play even during losing streaks.