What causes towns/game data to vanish for no reason?

[Rosie Moon]

Ok, so I've heard of people's towns suddenly disappearing, both cartridge and digital, and they've had to start over. Just this morning it happened to my friend and she was really upset, and it's left me wondering what causes people's towns to delete themselves like that? (The only thing I can think of in my friend's case is that her pen once leaked ink all over the cartridge...)
I really don't want my town to vanish too.

 

[Leopardfire]

I'm sorry that happened to her. She could have turned off the game without realizing she was still on the save screen. It's happened to a few people around here. It's an extremely slim chance that the game just corrupted randomly.

 

[golden moon]

Two friends of mine had theirs town vanished for no reason. They shuted down their 3ds, pulled off the cartridges (both have cartridge) then they reinserted the cartridge and started the game, their towns reappeared.
I think that this is a read error cause this game has lots of data to load, so people should try this before resetting the game