Expecting something to hurt doesn't really produce pain, but it can affect how you breathe and how you move. These two factors can increase your awareness of pain that is already present. Muscle tension from holding your breath and avoiding movements can make your pain seem worse. Relaxation is an important key in cases like this.
Anticipating a pain response can also delay muscle contraction, or sometimes the muscle contracts too early for the intended movement. This kind of muscle imbalance can lead to spinal instability. Pain and injury is more likely when the spine is unstable.