One aspect of the disclosure relates to altering a probability of fulfilling a game objective in a game space. The game objective may be associated with a set of potential reward items, the set of potential reward items including a first item. Probabilities of the first item from the set of potential reward items being provided to individual users as a reward for completing the game objective may be determined based on the rates of usage of the game space by the user. The probability of the first user being provided with the first item as a reward for completing the game objective may be determined based on the rate of usage of the game space by the first user.