I saw Grudge last weekend and liked the atmosphere but had no idea WHY anything was happening. I read this blurb about the original Ju-On today. Correct me if I'm wrong, but none of this was mentioned in the American version.
Some years back, a husband, obsessed with his wife's love for another man (a teacher), came home and brutally murdered her and their son. Concerned about the boy's absence from school, the teacher came by the house, where he bumped into the slain woman's ghost. The teacher then dropped dead of a heart attack and joined the ghosts of the woman and young boy. From that point on, a curse was passed to any future tenants of the house where the deaths occurred. The police are baffled, and the trail leads back to Detective Toyama (Misa Uehara), the ex-investigator who handled the initial murder case. But there seems to be no way to break the chain of evil….
The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents. ... The piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the light into the peace and safety of a new dark age.
~ Howard Phillips Lovecraft