No one is entirely in their right mind. Everyone has their own set of delusions. Delusions are comforting, and keep people from going any crazier. Perfect sanity is a burden far too vast for any mortal mind to bear. The nearest any humans get to it is a condition called paranoia, and that generally just decays into a more plausible set of delusions than is usual.

So you think you are perfectly sane? You are not. You are only very comfortable and convinced in your own set of delusions.