There are good reasons in response to: "Why we all think it's a great idea to leave our families at 18 and pay high rents so that we can live with strangers we found on the internet is beyond me," though personally I also don't believe that multigenerational housing is a symbol of failure, and often lets a person save a lot of money.
It's more difficult to maintain a romantic relationship when living with family (especially if both partners live with family), and it can also delay life skills (e.g. learning how to cook at home, clean, and generally learn to live more independently; though it's possible to deliberately learn this while living with family, it becomes a necessity to learn after moving out).
It's more difficult to maintain a romantic relationship when living with family (especially if both partners live with family), and it can also delay life skills (e.g. learning how to cook at home, clean, and generally learn to live more independently; though it's possible to deliberately learn this while living with family, it becomes a necessity to learn after moving out).