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Self-sufficiency is true sustainability!

And less capable than community sufficiency. No one person can possibly become competent in the same amount of skills and tasks that the population of a city, or a town, or a small village could. Nothing wrong with self sufficiency, as long as you're willing to sacrifice the skills of, say, heart surgeons and electronic engineers. Not the life for me, I'm afraid :P

Sustainability has many stages, many levels to it....You can look at sustainability in the choices you make as far as the time of showers or amount of stuff you throw away VS recycling. Though really thats not sustainability at all its simply LESS WASTE.
You can look at sustainability on an individual level, a community, city, state, nation. world and on. Obviously it is more efficient to have specialist working together so that whatever is being done is being done by the "best" but its still possible to have "specialist" who are part of a sustainable whole!
Steemit is actually a perfect example of a "sustainable" community in the sense that everyone is different yet we are all participating in the same thing in our individual way. We are all benefiting each other. Because the matter of fact is the MORE people participate regardless of if everyone agrees the community as a whole becomes richer.
Now if you take that to another level (like we have achieved in The Garden of Eden) we have a group of people who live for a common purpose and have common agreements AND we have specialists. So this small model we have mastered can be expounded to any scale. Its possible to have a city built upon community where every person has their own home, their own vehicle and makes their own money as long as the ENTIRE system/city operates on a sustainable infrastructure. Though for that to happen you would have to have basically EVERYTHING about how a city operates CHANGE.