I've always daydreamed stories. Original ones at first, though terribly derivative of whatever fantasy/SF book I'd read last. I started experimenting with fanfic in my late teens, and as chance would have it, got into a fandom where we were using the canon setting, but with all original characters. I didn't write fic using canon characters until I got into BtVS.

But I never, ever thought of fanfic as anything but an end in itself.