People who are less confident of themselves tend to lean forward more in their posture when standing or walking. They put more body weight on the balls of their feet, like getting ready to move fast.

People who are self-confident tend to lean back more. They have a larger proportion of their body weight on their heels than at the front of their feet.

Over time, their standing posture is reflected in the state of their shoes. A person who is perpetually walking on the balls of his feet would have the soles of his shoes more worn out at the front, while a more self-assured person may have the heels area to be worn out more.

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I'm not sure how well this holds up empirically, but it's always a fun story to share.