It is a standard trope, especially in fantasy role-playing games, that characters may be injured (or even killed) by illusionary creatures or obstacles that the victims believe in. I would like to know where this originated.
The rules for how this works are variable, even within a single game like Dungeons & Dragons. It may possible for illusions to kill a character outright, or an apparent death might merely lead to unconsciousness. "Disbelieving" the illusion may negate any damage it had done, or the damage might remain. What's more, the requirements to disbelieve an illusion can also vary a lot; it may be enough for the character to know that what they are seeing is not real, or it may be that, even if someone knows intellectually that what they are facing is illusory, they may still "believe" in it at a more visceral level and continue to take damage.
One particular view for how this works was expressed by Cordwainer Smith in his story "Think Blue, Count Two" (published 1963, well before the invention of modern RPGs):
The stranger went on in a very deliberate tone. "No bullet would come from my pistol, no ray, no blast, nothing. Nothing at all. But your flesh would believe me, even if your thoughts did not. Your bone structure would believe me, whether you thought so or not. I am communicating to every separate single cell in your body, to everything which I feel to be alive. If I think bullet at you, your bone will pull aside for the imaginary wound. Your skin will part, your blood will pour out, your brains will splash. They will not do it by physical force but by communication from me. Communication direct, you fool. That may not be real violence, but it serves my purpose just as well. Now do you understand me? Look at your wrist."
This is quite evocative, but it seems to be elaborating on a well-established idea. I doubt that this is the first instance; so what is the first example of being injured and possibly killed by an illusion?