Neck pain is often caused when the muscles and connective tissues in the upper back and neck region are not able to sufficiently support the weight of the head. Ligaments and muscles can be torn, sprained, strained, or damaged in some manner. They might not get exercises as often they need to be.
Another common cause of neck pain is poor posture. For example, you sit slouched over your desk at work all day with your neck and spine not properly aligned. The misalignment can place added stress on the neck and cause it to be strained beyond its normal range of motion.
Some people also suffer from chronic conditions, such as degenerative disc disease or arthritis. These conditions can cause pain in the joints in the upper spine and inflammation that triggers neck pain.