Change

" Oh. Betty don't you know there's  no such thing as forever?"

I think that this quote's main idea or theme would be change. It shows change because you don't live forever. If you want to accomplish things you have to change and do what you have to do because if you don't you'll never accomplish anything.  You don't have forever to be lazy and do whatever you want.  You have to try to succeed in life or life wouldn't be worth living. People need to realize that they can't lay back and ignore the real world when there are so many opportunities out there. This goes with Elsewhere because she died at age 15. So she only has that many years in elsewhere. If she wants to do things she has to accept the amount of change and adapt to it, so she can succeed. You don't have forever, so you might have to change to accomplish what you want to.