The indifference point is the central concept of GTO mixed strategies: when a player is indifferent between two actions, both carry identical expected value. For the defender, indifference is reached when the opponent bets at the exact frequency that makes calling and folding equal in EV. For the aggressor, indifference is created by the correct bluff mixing ratio that makes the opponent equally served by calling or folding. Mixed strategies exist precisely to maintain opponents at this indifference point, preventing any pure response from being profitable.