Someone much smarter than me (quite possibly Terry Rossio and Ted Elliott, although I can't be sure because for some reason I can't access their brilliant site at wordplayer.com) made an astute observation about identifying problems within a story or screenplay. Some problems are minor and can be easily fixed, others are a complete ball-ache and require a complete tear-down-rebuild in order to set right.
They compared it to building a house and then asking someone's opinion on it. One person might say, "I hate it, it's awful, it's completely the wrong colour." You can then spend an afternoon repainting the outside and it's all better. Someone else might say, "I love it, it's perfect, there's only one thing I would change--can you turn it round so it faces south instead of north?"
The reason I bring this up is I'm currently trying to edit a story, and have just stumbled over a very slight change that needs to be made... but which might well require picking up the whole damn house and turning it around. In essence, the first scene of this story takes place in the morning, at an art gallery, and then the story continues through the rest of the day and the events therein. This time factor is pretty much essential to the story (it wouldn't be feasible to, say, extend the narrative over an extra day). But it's just occurred to me that... why would anyone schedule a wine-and-canapes reception for the opening of a new installation at an art gallery, first thing in the morning?
It's a really daft point that completely escaped my attention up until this moment. And it's easily enough fixed--nothing more than changing the word "morning" to "evening" on the first page. But that little change is going to have an impact on the rest of the story. Instead of taking place over the course of a day, concluding in the evening, it would have to take place during the night and conclude early the following morning.
Doesn't sound like a bit problem, does it? After the art gallery, the character goes to a market. Would said market still be open in the evening? Whilst there, he meets a couple of auxiliary characters, including a pair of young children. Would they still be awake and out of bed at that time of the day? Would the subsequent actions of the main character seem more or less suspicious if he's sneaking around at midnight rather than early afternoon? And so on.
Stupid little niggly problems, none of which are insurmountable but all of which are flipping annoying and will take more effort than expected to fix. Too many problems of that type can make you seriously consider just knocking down the whole stupid house and having done with it.
But, of course, there's always the possibility of a quick-fix... I've not found one yet, but I'm working on it. Sticking with the metaphor, there's a chance we can just take the front door and the back door off the hypothetical house and swap them over, which technically at least would mean the house is facing south instead of north...