I realize two things when I breathe deeply.
One: I rarely breathe deeply.
Two: When I do remember, pause, and breathe, I become aware of the prison in which I live--jaw set, shoulders tensed, throat rigid, back hunched. That's a straightjacket of tension right there, and one we all (well, most) seem to put on every day, unquestioningly and blank-gazing docility.
We have been brainwashed into automatic tension, and have fallen in love with our captor. Breathing might be the mightiest, cheapest, quietest, and most powerful form of rebellion we have.