@Daisyl, I'd never heard the term "Eternal Terrarium" so I just had to google.
I think it's just a name fad name/label ... possibly to try and get people interested in terrariums?
https://www.google.com/webhp?s...
And, yes ... plants in terrariums can and will die without proper moisture, light and nutrients ...
ask me how I know.
"Eternal" may not be the best label to stick on a terrarium.