The placebo effect shows that belief and expectation can produce measurable changes in symptoms and well-being. A treatment with no direct active ingredient can still trigger real responses if the patient expects benefit.

This does not mean illness is imaginary. It means mind and body are more interconnected than simplistic models assume. The placebo effect is one of the clearest demonstrations that meaning, expectation, and context can shape physiological experience.

Reference:

Wikipedia: Placebo

https://en.wikipedia.org/wiki/Placebo