The nature of a story is to explore a "world" out of balance, or more specifically, a "Story Mind" out of balance. There is something out of whack that is throwing EVERYTHING off. The purpose of having four throughlines is to provide a sufficient number of differing perspectives to make obvious where/what the problem is. Any single perspective can SEEM to be correct but, when shown in the alternative contexts, may be completely out of line. The purpose of having all items present in every story is to cover all the places where a problem might exist. If you leave something out, it will seem to leave a "hole" and the audience will usually pick up on it.