We often squish our collar bone onto our top rib, either as we try to hold ourselves up or as we slump. When we do this we make it hard for the ribs to move with breath, and for our arms to freely release from the whole torso.
It makes it very hard to fly if you do not have your full wing span.
Remember change comes with the power of our thinking. I find just picturing and allowing that space between the top ribs and the collar bones makes a huge difference in how I breath and how I use my arms. Somehow it also gives me more clarity of my pelvis.