The shoulder is always a joint at risk, so to speak. It has the most motion of all the human joints, with freedom in many planes. The unique anatomy of the shoulder gives us motion and stability both, and these functions are interdependent. The bone structure of the shoulder joint would make you wonder why the arm doesn't fall off the body. There is a thick cartilagenous lip or rim called the labrum which converts the flat articular surface into a cup-like shape for the roundish humeral head to lie in. But it is still quite loose, so this is why the muscle componant of the shoulder is so important. May muscles are involved and the names are not important to this musing. What is noteworthy is the function of the so-called rotator cuff. This flat thick tendonous structure is actually part of the tendons of several muscles melded together. It allows the shoulder to be placed and pulled into the socket so it can more overhead. This tendon, like many others is prone to degeneration with age and subject to damage and tear.
The really good news is that at least 50% of people with significant shoulder pathology can be healed or at least returned to function with rehab and not surgery. I spoke with a friend today whose chronic biceps tendonitis and eventual tear was treated with therapy alone and years later he has full function without pain. I myself, have a complete tear of the rotayor cuff. Therapy taught me to use my shoulder correctly and with heavy use I have had no trouble for two years until the current overuse/tear occured. I am delighted it is resolving well with massage, careful stretching and heat with anti-inflammatories. Shoulder problems occur but should not be greatly feared in my opinion. Give rehab a try!