Today you're going to take a very simple look at your standing (and breathing) at attention posture as an expression of saying 'YES', vs your default tension-filled posture as a 'NO'.
Biologists classify the behaviours of living organisms as either avoidance and approach types. The former involves tightening-up and closing-down your body and breath (and by extension, emotions and thinking), while the latter involves opening and softening (again, at all levels of your mind).
All reactivity (and the thoughts produced from it) leads to a NO posture ("I don't like it!"), while standing at attention involves deliberately putting yourself into a YES posture (overriding years of habit and the dictates of your emotional reactions and thoughts).
This deliberately chosen physical YES is not a static, set-and-forget state! You have to keep choosing it, in large part because there is such a deep habitual and unconscious NO going on all the time in the background. At first, until you find and change this habit, you need an ongoing Fresh YES.
As you choose to stand/sit and breath at attention, feel it as deliberately saying YES towards things just as they are, irrespective of how you feel or think about them.