Mid back pain occurs in the thoracic spine which is the least mobile area of the spine due to the rib articulations. The ribs form a cage that attaches to the spine at the back and to the front attach to the sternum. The 11 and 12th ribs don’t come all the way to the front but rather float attaching only to the thoracic spine.
Due to the limited movement of the thoracic spine, it's not as vulnerable to wear and tear as the more mobile areas of the neck and low back.
It can however be an area of pain of many different causes. Due to the organs that are housed under the rib cage it is always better to see a health professional whenever someone experiences continued or reappearing pain.
Poor postural habits especially those postures which require a lot of forward bending or sitting at a desk with forward head posture, can place a lot of stress on the thoracic spine. This can lead to distortions and abnormal carriage of this part of the spine which in turn can cause significant discomfort and fatigue or mid back pain. The rib articulations are also often adjusted as they also tend to become subluxated and become a source of inflammation and aberrant movement.
Distortions in the thoracic spine will also dictate how the neck moves and is held. Often the distortions in the thoracic spine originate in the lumbar spine and pelvis.