In Wanting, needing, yearning, dreaming I found myself saying that post-hoc understanding of what you've written can be immensely useful, much more so than reading a textbook about how you 'should' do things before you write. The latter is like seeing a new fashion in a magazine and buying the dress to wear without trying it on: who would do that? The former is like trying it on in the shop to see how it looks on your body: as we all know, there are always some current fashions which are just wrong for our particular build. By the time you've written a piece and really revised it, you know it extremely well. If you then try some ideas about how good writing works on it, you're much more likely to decide whether they're the right shape for your work. If those ideas don't seem to fit, you're more likely to have the confidence to discard them. What leads to disaster is to be so sure the rules - like the fashion - must be right and your body must be wrong that you wear something that makes you look dreadful or, worse still, sign up for plastic surgery.
Not that writing to fulfil technical brief - as an exercise - doesn't have its uses. At the most basic level it is just that - good exercise - to get your brain rootling out words for reasons different from your usual ones. And more widely it can be liberating to give up on the sometimes paralysing demand to write a great story, and concentrate instead on something easier to pin down and less daunting. One of my most successful stories ever began as no more than an exercise in shifting point-of-view. And as I was talking about in Rhyme and un-reason, technical constraints can actually lead to your mind working more creatively. Perhaps it's not just form that can make a sieve to catch certain kinds of material, it's any kind of technical structure.
Fundamentally, the reason we learn best from post-hoc understanding is because that mirrors the actual process of writing: we write, then we see what we've written, and it's the technical/editorial half of our writerly self who has a long, hard stare at the image in the fitting room mirror. That understanding is all about the fit between the structure of the clothes that fashion is offering us at the moment, and our real, actual bodies. And to all the people who'd say that beginner writers need rules before they write, and should only be allowed to discard them once they've grown up, I'd say, Nonsense. What beginner writers need is help: they need ways to circumvent self-consciousness and un-confidence and allow their writing to emerge, and then they need someone else standing at their shoulder and talking about what the fitting room mirror's showing them both. What they don't need is someone telling them before they even get into the shop that green will never be their colour, or that they can't wear long skirts because they're too difficult to wear. The human body - like the writer's mind - is never that simple.