Well, it's not much simpler than I turned on my keyboard, looked at it for a while, messed with it for a bit, spliced together a few preexisting compositions, and you end up with something like this. You think to yourself, "Hmm . . .", and you write it down somewhere. Later, you come back with your mission to lay down a nice fingered bass line. You succeed, and the rest of the song simply falls into place . . .