Variable Rewards
Unpredictable or random rewards are more addictive than a predictable schedule.
Casinos know that slot machines are more addictive if they pay out a random reward at unpredictable times. If people always won back 80% of their money on each pull of the lever, it wouldn't be an exciting game and wouldn't be addictive. It's the unpredictable and random nature of the rewards that keeps people playing with the hope for that rare big jackpot.
A constant or predictable schedule of rewards is not very exciting. This is why games often randomize the rewards that you receive for finishing a level or defeating an enemy. By making the rewards like a slot machine, they are trying to make the game more additive. They may also be trying to extend gameplay by making you grind longer to get what you want. If you need a certain item, but it only appears as a reward 5% of the time, people will keep playing over and over with the hope of getting that rare item. If the game has limited energy and forces you to wait to play then people may end up paying money to skip the wait.
A constant or predictable schedule of rewards is not very exciting. This is why games often randomize the rewards that you receive for finishing a level or defeating an enemy. By making the rewards like a slot machine, they are trying to make the game more additive. They may also be trying to extend gameplay by making you grind longer to get what you want. If you need a certain item, but it only appears as a reward 5% of the time, people will keep playing over and over with the hope of getting that rare item. If the game has limited energy and forces you to wait to play then people may end up paying money to skip the wait.
Citations and Sources • Why are Video Games Addictive?
• Behavioral Game Design
• 5 Game Mechanics that Make Games Addicting
• Wikipedia :: Reinforcement
• Behavioral Game Design
• 5 Game Mechanics that Make Games Addicting
• Wikipedia :: Reinforcement
Examples
Love Nikki-Dress UP Queen"item drops on levels are never guaranteed, requiring players to waste stamina on grinding"
Chuzzle 2"there are spots on the level map that give you a random reward when reached, and completing the daily puzzle gives you a random prize"
Pikmin Bloom"there are a few types of seeds (particularly event seeds) that give you a random pikmin when it finishes growing, so it's impossible to determine when or if you'll be able to finish an event with limited time pikmin"
Kawaii Home Design"So. Many. Rewards. And there's mostly just random and end up being useless. I cannot stress this enough."
Papa's Mocharia To Go!"Minigames can be played to unlock random clothing items. These minigames are optional."
Food Street - Restaurant Management & Food Game"Events"
Minecraft"Some achievements come with optional skins for your player character."
Animal Crossing: Pocket Camp"Some events that you need to do repetitive tasks to complete have a fortune cookie as their reward, which gives you a random item (the collection of which depends on the cookie, that much you know from its name and appearance.)"
Baseball Superstars 2020"you can make your own quests which can give you tickets to summon random trainers."
WitchSpring2"some random material grinding but not that hard."