Here is Asia appearances are everything. You dress well, carry yourself well (in Thailand you smile, smile, smile) and are always clean and well groomed, if you're not it's noticed immediately; you will be shown less respect, tried to be taken advantage of more, and in general be subject to stares and ridicule. Which is why everyone seems to have excellent posture here. Everyone except the obscenely rich have amazing posture and straight backs.
Actually, you make a good point. Our outward appearance tends to be a reflection of our internal state of being. But changing our external attitudes can over time have a subconscious influence on our internal states as well. It's the whole "fake it till you make it" attitude. It's not immediate, but with time and consistency, you can change your state of mind and attitudes by first reflecting them outwardly.
Incidentally, here's why you have to take care of yourself! (I found this yesterday, talk about timing.)
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