impenetrability

If you want people to think that you are saying something very important, then say something impenetrable!

The sight of the wall of water outside reassured me, giving me the idea that it made very little difference whether I stayed with her, or set out alone on my journey that had neither visible starting point nor destination. It didn't matter: since, however closely I became involved with another existence, my own world would always remain secret, inaccessible and shut-off; nobody would ever see me, except as a dim, changeable, wavering shadow, through its impenetrable, semi-opaque walls.