Well obvy the original saying is "the sky's the limit," but I think that's naively optimistic. In general, your limits are much lower. Wouldn't it be better to be a little more realistic? In fact, I recently read that people who have low expectations are the happiest, so if you say "Whelp, the ceiling's the limit" but then find yourself in the sky by some lucky chance, well, imagine the elation!
Or you could think about it this way: in astronomical terms, limiting yourself to the sky is relatively pitiful--you could go much, much further. Ha!