"We do not inherit the world from our parents. We borrow it from our children." 

Native American Saying

I've seen some other versions of this saying, ancestors instead of parents for example. To me, it is a very powerful proverb in its difference between 'inherit' and 'borrow'. When you inherit something, you own it, and as such you can do what you want with it. When you borrow something, you don't own it, you have to return it so you have to take care of it because you are entrusted with it. I think it's a great mentality to have when it comes to planet Earth, because it is the only planet we have and when you think we are borrowing it from your children and grandchildren, it makes you take care of it that much more.