One of the best known POSIWID arguments is about the assassination of JFK, and the subsequent shooting of Lee Harvey Oswald by Jack Ruby. Following the assassination, political power shifted from Chicago to Texas, so this must have been its purpose. The effect of Ruby's act was to silence Oswald, so this must have been its purpose.
Ruby perhaps thought he was acting alone and spontaneously, and his friends still insist on this. But for POSIWID, conscious intent doesn't matter. Perhaps someone put the idea of retribution into Ruby's head; perhaps someone else got Oswald to smile, knowing that this would trigger Ruby's anger.