I don't think you're supposed to know that, if you're superstitious you will assume that it's a family curse, otherwise, well, it just terrible events that... just happened to a family, no reason behind.
For me, it was all about each individual story (including the protagonist), how it's told and how the "feels" hit you like a train (heh). There was two or that felt bland (the actress and the painter) but the rest was just heartbreaking. The one of the guy that worked at the cannery, Jesus Christ, that one is the definition of depression. The ending was the toughest part because after revealing what happened to her family members (and how sad their demise was), you're hoping that she breaks the "curse". It's even more sad when it's revealed that it's her kid that is reading her diary.
Obligatory gif: