I posted this comment on a friend's journal a little while back, and after doing so got permission to repost it here, as I thought it touched on a side of the experience of alternate identity that hasn't been touched on much before. Not other/fiction as simple metaphor ("I'm like a dragon because I hoard stuff and like shiny things"), nor as a physical/metaphysical reality ("I'm a dragon because in a past life I was a dragon/I have a dragon's soul"), but something trickier to grasp, in parts allegorical but also more significant, more central than a metaphor: I am a dragon because when I look at the idea of dragon, something very core about it clicks with me and reminds me of me.
I feel like whatever else you say about it, whether you believe there's an additional explanation... that's the heart of it, for a lot of people. That's the level on which they click with the concept. Or at least, that's what seems to make sense of the idea for me.
(Also, anyone notice that LJ seems to have brought back the Deleted Username Strikethrough, replacing the Boldface that followed in the wake of LJ's mass questionable-journals-deleting spree? Interesting, kinda....)