Although you may not stumble across a Martian in the garden, you might stumble across yourself. The

Although you may not stumble across a Martian in the garden, you might stumble across yourself. The day that happens, you'll probably also scream a little. And that'll be perfectly all right, because it's not every day you realize you're a living planet dweller on a little island in the universe.
----Jostein Gaarder, The Solitaire Mystery