I got a lot of practice rowing in small boats filled to the gunwales with gear, in wind with choppy seas. If you waste a stroke by trying to muscle it or by inserting your oar into the water at the wrong angle or by digging too deep, you loose several strokes. Efficiency is the only way to get headway in rough seas. Those were the days.
We worked on this all wooden boat and took really good care of it. When we tied the boat up to the dock we used a method called a spring-line. This requires four ropes (called lines on a boat). Each rope if tightened by itself will pull one part of the boat in toward the dock and push another part outward. By balancing the tension between all four lines there is a magic spot where all the ropes are a little slack, and yet the boat is sprung away from the dock. If you crank down on all the ropes or even just one, the beautifully finished and finely tuned boat will crunch against the dock and your hair will stand on end. But if you find that perfect balanced tension the boat floats effortlessly just off the dock.
The coast guard has an O.K. picture of it.
Think of your shoulder as a boat floating in water tied to the dock using a spring-line. The ropes are the little muscles that go between the proximal part of your upper-arm bone (humerus) and both the front and back parts of your shoulder blade(scapula). All the ropes must be loose and yet balanced with all the other ropes, and then the shoulder will float without pulling away and without crunching.