I love those scary-cool moments when stuff I put into a maunscript early on suddenly all comes together. I imagine it's much more rattling when it happens over the course of a series.

I don't think it's (entirely) one's brain pulling a magic trick. I think it has to do as much with craft as the rest of writing--the more one consciously makes an effort to weave in details and scenes that become very important later, the more trained one's brain is to go and do the work behind the scene, so epiphanies seem to pop up out of nowhere.