my doctor said i was cured, and i believed him
It's more than just that, though. Your brain and body are in a constant feedback loop; fake smiling makes people happier, high prices make food tastier, and taking placebos can regenerate muscle tissue. Imagining a physical workout (with electrodes making sure muscles aren't actually moving) can significantly increase your muscle growth. Whenever a new medicine is tested, it has to perform better than placebo instead of baseline, that is how relevant the placebo effect is
It's more than just "between the ears". The brain has a huge effect on how we exist in the world