Another easy way to get people to come back is by adding expiring content. This could come in the form of points or leaderboards that reset each week, certain virtual goods that can only be bought or won for a certain duration, or alternative rule sets that are only available for a limited time. This is an area the music business has traditionally been good at, from flash merch sales, to ‘early bird’ ticketing schemes. There’s a big difference though: in games, expiring goods exist to drive habit-forming behaviour, so that people get hooked. The way you need to think about it is as designing someone’s experience, rather than simple tricks to extract money from them.