It can be. And it's not all positive. The nocebo effect can be so strong, that people actually die because they think they are cursed (other examples: Covid vaccines, statins, ...).

Any generalised statement about the effect of placebo/nocebo is difficult, because some portion of the effect is regression to the mean, and relatively little is known about the mechanism of action (e.g. there is some indication about a genetic factor).

Not disagreeing with you that it may not work for you, but it may work quite well for some people. Acupuncture being a prime example.