Have you ever been urged to "Stand up for your beliefs?" Or perhaps you've told someone to "Stand tall." We describe cowards as people "spineless", and admire those that we see as "upright". References to posture are sprinkled throughout language. We stand up, stand firm, stand out. We take stands, sometimes making last stands.
The positions of our bodies makes a huge difference on every other aspect of what we do. Athletes, including martial artists, are keenly aware of how good posture and stance impacts balance and performance. A football player that is centered is harder to tackle compared to one that is off balance, for example. But it's not just athletes that consider posture essential. One of the first things a music student learns when starting to sing or play an instrument is how to stand or sit correctly. Companies pay ergonomics experts large fees to teach their employees how best to sit or stand when doing their work, and often pay for desks or chairs to facilitate good posture.
The way we stand also communicates intent and attitude to those around us. Think of two people: one with hunched shoulders and a bowed head, and another standing upright with their head held high. Which one seems more timid? Which seems more confident? By observing posture, others can gauge how alert we are, how engaged, or how relaxed.
And just as other people can make inferences based how you sit or stand, you can also use it as a reminder to yourself. So as you go through your day, be conscious of your posture -- what it does for your balance and health, what it tells others, and what it communicates to yourself.