You don't know that for sure! Are there any mysterious cases of people just being normal one day and then the next up and like, uhhhhhhhhhhhhh, and not wanting to do anything but just hanging around?

'Cause that's what happens when a Shadow eats their soul.

[ THE CORRECTNESS OF THIS ENTIRE CONVERSATION IS DUBIOUS BECAUSE IT'S COMING FROM JUNPEI, but you get the gist. ]