When you are expecting pain, like the moment just before an injection, your brain regions that process nociception change their activity. That is, you simulate pain and therefore feel it. This phenomenon is called the nocebo effect. You’re probably more familiar with its counterpart, the placebo effect, which relieves pain using a medically ineffective treatment like a sugar pill. If you believe you’ll feel less pain, your beliefs influence your predictions and tune down your nociceptive input so you do feel less pain.
