It's most notable with song lyrics: you know the effect you're going for, you know the cadence, how many syllables, what you've got to rhyme with (if you can be bothered with that sort of thing). Then you pick up your pen, phone, laptop or whatever and the words just don't fit the shape. Sometimes they end up mangling the rhythm, sometimes it's a stubborn refusal to make the point you want to make. I often find that the most fitting set of words for the tune is not the ones I would have chosen to express the idea. For a case in point, take Always. In the chorus, the line originally went 'to stay your arm...' Now, it's 'stay inside your arms', and that expresses not just a slightly different idea, but pretty much the opposite one altogether. It's sometimes easier to let someone else write the words, rather than cast around for the best way. And I would go as far as to say that it can be easier to sing someone else's words, as well, because you sort of put your meaning into them, rather than, as with your own lyrics, trying to get them to mean what you want them to there on the page or in the song. I, sadly, am no singer, but I do enjoy the occasions when I get the opportunity to sing, even if no one else does. My lack of technique (by which I mean my wince-inducing tunelessness) means that singing to someone is a most dangerous gamble, even if the person is a little one and unlikely to have high standards of musical correctness.
I suppose the other observation is that you can sing a song of thirty or fifty lines, and there can be only a couple that carry any real meaning for you as the singer. I put song lyrics, quotations from my own and others' writings and all sorts of stuff on the front page of this website partly because someone once told me that frequent updates led to more google-juice but also because those words might have struck me as particularly relevant or powerful that day, perhaps I was absently singing them just before picking up the laptop or for some reason that was what I chose to listen to. In the case of Snow those lyrics are not mine, but the idea - of a persistent thinking of someone, not a happy, settled relationship but a desperate, denied yearning - came from me. Anyone who has read what I have written will instantly be able to identify the model for that thought. So they're not my words. But, for the most part, they get the point across in a way which I could not have achieved. I also think the tune has some merit!
Does it happen when I'm writing These Matters? As I have mentioned before, I don't have a very settled plan for the events of the books. In fact, book IV (title to be decided fairly soon; I have rejected Rebellion (Lies) as someone else seems to have thought of it already) has proved a difficult technical challenge because there are some unavoidable historical hummocks that constrain the plot, and I have had to go into great detail in the research - buying and reading books and pamphlets of which I can be fairly sure I am the only living owner - to get ideas of how to untie some of these knots. My most frequent experience of trying to plot carefully is that as soon as I have anything approaching a settled plan, a scene emerges which forces a substantial change almost immediately. So it's quite free-flowing, in that sense. Not, perhaps in the sense of words written per day or week, though. I've also seriously miscalculated (or misread?) my characters' motivations in some cases, most notably not realising that Edward Strelley and Elizabeth were falling deeply in love with each other until I was told by one of my mates who had read the books. I don't feel like I'm writing These Matters. When I'm able to give it the time, it writes itself.
When to the sessions of sweet silent thought