If I’m watching a movie, the second any character is revealed to be either:
1. A shape-shifter or
2. A double agent
… that’s the moment I groan and check out. I am not going to invest any energy in a movie that intends to confuse me.
Oh, and while I’m complaining, add all those Mission Impossible movies to that list. I’m not going to follow each scene on two tracks: the one in which I believe that’s Tom Cruise, and another in which I guess which evil character has donned an absurdly accurate Tom Cruise mask.