This is a bittersweet video from Lembeh, Indonesia, of diver Pall Sigurdsson helping a small coconut octopus trade the plastic cup it's taken refuge in for a proper, protective shell (they're called coconut octopuses because they often use coconuts as well). Some more info while I wish Captain Planet was real and mad as hell:
While a shell is a sturdy protection, a passing eel or flounder would probably swallow the cup with the octopus in it, most likely also killing the predator or weakening it to a point where it will be soon eaten by an even bigger fish.
We found this particular octopus at about 20 meters under the water, we tried for a long time to give it shells hoping that it would trade the shell. Coconut octopus are famous for being very picky about which shells they keep so we had to try with many different shells before it found one to be acceptable.
Well that's a happy ending. And if they hadn't intervened, what -- a fish would have eaten the octopus AND cup and continued this circle of sadness? We have to break the cycle! Otherwise there won't be any more octopuses, and when your grandkid sees a hologram of one they'll ask 'Is it really true there used to be aliens on earth?' as they twist the top off another plastic bottle of filtered air.
Keep going for the video.
Thanks to Abby C, who agrees octopuses deserve better.