You are either preventing or not preventing illness all the time. There is no such thing as benign neglect. The feedback loop is inescapable. Rather than considering that a threat, we can create a new model of well-being that gives you much more control over your health for life.
While some negative outcomes have nothing to do with patient expectations (adverse events are known risks with all treatments), the "nocebo effect" is especially pernicious because it can contaminate good care and is preventable.