There's no 'mystery' (to/as to/about) why we're here. = It's no 'mystery' why we're here. [=we know why we are here]
His success is something of a 'mystery'. = His success is a bit of a 'mystery'.
We'll reveal the identity of today's 'mystery' guest after these commercials.
(..) My mentor taught me everything about the Force. Even the nature of the dark side. You know the dark side? Anakin, if one is to understand the great mystery, one must study all its aspects, not just the dogmatic narrow view ofthe Jedi. If you wish to become a complete and wise leader, (..)2005 Star Wars: Episode III - Revenge of the Sith