This is a very important concept for you to understand. We now know from MRI research studies that many asymptomatic (no pain) people have rotator cuff and other tendon and cartilage tears, and these increase with age. This is also true in other parts of the body. So the bottom line is that a tear visualized on an MRI may not be causing a patient's pain. This leads to much unnecessary surgery. I treat many patients who have had unsuccessful surgery. 
Remember what I heard a chiropractic doctor say " I can take an MRI of your phone and it would show me everything in the phone, but it would not tell me if your phone was ringing" 

http://bangordailynews.com/2014/11/06/health/blogs-and-columns/got-shoulder-pain-dont-assume-its-a-rotator-cuff-tear/