Placebo in a nutshell: inject someone in pain with morphine. do it repeatedly over time. once, without telling them, inject them with saline instead. their brain will respond as if it was morphine and continue to block the pain.

The whole "people believing X so X happens" is a perverse co-opting of the placebo title.

And, just for fun, if you give a patient naloxone (opiate blocker) before giving them the saline, their brains won't interpret it as morphine. naloxone blocks placebo response. in case you missed that, read it again: naloxone blocks placebo response. (and once more: placebo means a very narrow thing. it means your body responds as if it biologically received the medicine it had been receiving -- it does not mean any new age "think your way to better health" mumbo jumbo).