Subjects of myth and legend, dragons are fascinating creatures; as mysterious as they are terrifying. Outsiders don't know much about them, and most of what they do know is dubious at best. And that's just fine with the fire-breathers; the only ones that should know about dragon business are dragons themselves.
But being an outsider himself means that Spike has missed out on some vital knowledge. For most of his life he's been lucky that that fact was little more than an occasional inconvenience, but the thing about luck is that it eventually runs out. Knowing nothing about what he was and where he came from was bound to bite him in the ass someday.
However, perhaps his luck hasn't run totally dry just yet.