"In a novel, the narrative moves from start to finish, from beginning to end. But within that framework time can be juggled, treated with careless disregard - the story can progress, can dip backwards, fold up, expand. What matters is the satisfactory whole defined by Frank Kermode: 'All such plotting presupposes and requires that an end will bestow upon the whole duration and meaning.' For a novel to work, you want to come away from reading it with the sense that everything has gathered towards a convincing conclusion - not one that necessarily ties up every loose end, but one that feels an integral part of what has gone before. It must make sense of the space between the beginning and the end. You start reading a novel with no idea where this thing is going to go; you should finish it feeling that it could have gone no other way.
The novelist would like the writing process to be thus; it is not - or at least not for me. I do need to have a good idea where the thing is going - I won't have started at all until a notebook is full of ideas and instructions to myself. And I will have achieved the finishing line only after pursuing various options, wondering if this would work better than that. The reader should have an easy ride at the expense of the writer's accumulated hours of inspiration and rejection and certainty and doubt."
From Ammonites and Leaping Fish: A Life in Time by Penelope Lively.
See also Robertson Davies on this subject.