Yeah i know what you mean, it just seems too simple an explanation for something that is so widely used!
For some reason one of my old teachers (a few years ago now) used to say that “break a leg” was said kind of as a deterrent because that is the complete opposite of what they want to happen, stupid explanation i know, but at least there are some more plausible ideas here!
No, that is the most plausible explanation. It is the superstition route. Don’t say “good luck” because that will bring on bad luck. Wish them bad luck so thereby the opposite will happen.
Yup. And you’ll find the same “logic” elsewhere. In Norway you don’t wish a fisherman good fishing, cause that will cause the opposite, you wish him crap fishing, “skitt fiske”.
This is an example of reverse psychology as applied to the ever-present evil spirits. Wishing out loud something opposite of your real intent will trick the spirits into not causing harm.