Nothing last forever.

Nature, things that we created don't last forever as we seem. 

But mother-nature is self-sustainable. Without the presence of a human on earth, trees and vegetation would flourish.

Sustainability of creation depends on two questions:
1. for What?
2. for How long?

Sustainable building - All building needs maintenance to sustain or keep up. Even a namely "self-sustain" building would need its system maintained. 

If a building does not require maintenance to sustain, there is no purpose in building it. Self-sustainable creations are not built, they are god-made - mother-nature: tree, grass, shrubs, river, mountain.   

Sustainable business - Your intention will tell you almost everything in up-keeping a business. If you are doing something that is not enjoyable, things aren't sustainable as the driver (You) are missing out part of yourself when you do the work - your time, your soul, your energy. 

Balance is the key to sustainable business. A condition where you gain something from your creation serving a purpose and it balances out the effort you have put into your work. And I am not talking about exponentially gain on either business or yourself along the period doing work, that is growth, which differs from sustainability.

Sustaining a habit - An initial drive of doing something is important. Setting out time-frame that we think we will be able to do something in repetition makes us review why we have to do the thing in the first place.

So, next time when you are about to do something or meet something that proposes sustainability, ask "for how long?" and "for what?".