Plotting is more difficult. If a group of people is torn apart by internal dissensions, they need to be quarreling before it -- and they need to do something while they are quarreling. Otherwise you end up with incredible weak effect of their falling apart in the first scene. Since it has to be important -- or it has no place in the story -- it is weakened if the readers can't see the power of what shredded it. Much more logical to assume that it never was that strong in the first place, because they saw it only in broken form.
Or the characters meet in the opening and some events need them to have worked together enough that trust would be plausible. And they can't exactly work on stuff in the abstract.
It can be very annoying when the Muse decides that what is clearly an event in the middle of the story is so very fascinating.