Oh the box isn't so black. That's not to say that everything
  will make sense but consider:
  a) We're communicating
  b) We have generalized knowledge of patterns observable through
  behavior.

  Yes, there is lying. Yes, many of the methods used to
  "mind-read" fail. In fact, I say it frequently:

  MINDREADING IS IMPOSSIBLE

  But... you _can_ understand them and have a seat and look around
  their house, once you understand their own patterns.

  That's not to say they won't surprise you but up to a limited
  point, it's certainly possible. And the more patterned someone
  is, the easier it is to step in their mind. Might not see
  everything but you can see a lot.