Complete the Collection
The urge to collect all the items, achievements or secrets in a game.
The desire to collect things is a strong urge that game developers often exploit to get you to keep playing a game with the hope that one day you'll find all the rare items and have a complete set.
For people who collect things, the collection can have significant emotional value. It may connect them to something that they enjoy or feel strongly about. Some people collect for the thrill of the hunt, others may collect because it gives them a sense of security or control. Others may derive great satisfaction from having a complete set and feel anxious when they are missing a piece of a set.
All of these psychological effects contribute to making you keep playing the game, even if the "playing" of the game is not enjoyable anymore. If game developers are constantly releasing new content, then the players are always needing to "catch up" and may feel like they need to spend money to do so.
Sometimes reaching the 100% completion rating in a game can take hundreds of hours of additional tedious work beyond the normal scope of the game. Sometimes, some of the collectable items are only available via special events, and because players may have a fear of missing out on those items, they will continue playing and paying, even if the game is no longer fun.
For people who collect things, the collection can have significant emotional value. It may connect them to something that they enjoy or feel strongly about. Some people collect for the thrill of the hunt, others may collect because it gives them a sense of security or control. Others may derive great satisfaction from having a complete set and feel anxious when they are missing a piece of a set.
All of these psychological effects contribute to making you keep playing the game, even if the "playing" of the game is not enjoyable anymore. If game developers are constantly releasing new content, then the players are always needing to "catch up" and may feel like they need to spend money to do so.
Sometimes reaching the 100% completion rating in a game can take hundreds of hours of additional tedious work beyond the normal scope of the game. Sometimes, some of the collectable items are only available via special events, and because players may have a fear of missing out on those items, they will continue playing and paying, even if the game is no longer fun.
Examples
PewDiePie's Tuber Simulator"Pixelings (including rare prisma) and Craniac furniture (some event specific) is tracked on the profile There are new event masks for all 3 week interval events, many people grind to get them all (you can only get 4 or 6 masks from previous events of the same type during one event)"
Baba Is You"Completing every puzzle puts a stamp on your save file"
The Battle Cats"In the early game, grinding for treasures, a completely luck-based reward, is basically mandatory, if you don't get them, you will have an extremely difficult time dealing with the enemies. The game does though, give you the option to skip levels and a guaranteed chance of obtaining treasures for items."
Geometry Dash"Achievements unlock cosmetics, locked cosmetics are shown in the cosmetics selection"
Garena Free Fire MAX"There are some paid skins achievements that incentivise you to complete the set, the game doesn't really pushes it on to you but it's there"
Angry Birds 2"You can complete clothing collections for an award"
Brawl Stars"getting all brawlers and cosmetics. it doesnt urge you but it wants you to play more and collect more skins"
World War Rising"Having a full equipment set will provide extra bonuses, but even those need to be activated with more resources."
Clash of Clans"Collection of every rare obstacle and decoration is subtly encouraged. At one point in time it was very easy to do this, but as time goes on, the requirements for collecting have started to require spending more and more real world money in order to maintain your collection."
Block Blast-Block Puzzle Games"The classic 3 star progress."