HDRL is running an analysis of loot systems in modern games. They talk about how in-game rewards, formerly the domain of RPGs and adventure games with powerups, have expanded to exist in every genre
, as achievements and unlockable bonuses have become standard fare.
"For the majority of gamers, once the novelty is gone, they move on. To keep players interested, rewards are required. ... The Diablo series is a perfect example of the theory in effect. Just as in the story of the donkey and the carrot, a game's rewards cannot be too frequent, nor can it be too infrequent. If rewards are too frequent, they lose value in the eyes of the player, and they lose interest. If the rewards are too infrequent, the player loses sight of the carrot, and likely loses motivation to keep playing."