Sometimes a person can have a response to a placebo. The response can be
positive or negative. For instance, the person's symptoms may improve.
Or the person may have what appears to be side effects from the
treatment. These responses are known as the "placebo effect."
Research on the placebo effect has focused on the relationship of mind
and body. One of the most common theories is that the placebo effect is
due to a person's expectations. If a person expects a pill to do
something, then it's possible that the body's own chemistry can cause
effects similar to what a medication might have caused.
With Covid-19, if someone has the expectations of developing the 'reported Covid-19 symptoms' when they have tested positive for the PCR test, then they can very well suddenly find themselves with Covid-19, even though Covid-19 might not actually be a unique virus, but in truth an agent of psychological warfare.