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The placebo effect has an evil twin known as the nocebo effect. This is when the expectation of harm or pain becomes a self-fulfilling prophesy, even in the absence of any known physical effect. One candidate for the nocebo effect is the discomfort some people report experiencing after using mobile phones. Scientists have failed to identify a physical cause, so it's possible the adverse effects are caused by negative beliefs about the technology.
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Christian Jarrett (30-Second Psychology: The 50 Most Thought-Provoking Psychology Theories, Each Explained In Half A Minute)