The clip comes from SpongeBob Plug 'n' Plays (With Shrek), a fan made parody video by creator AquaticNeptune that riffs on SpongeBob and old plug and play games. Lines from those videos circulate on soundboards because they isolate familiar characters saying absurd things out of context. This marshmallow line survives for the same reason, as a short, self contained declaration of intent that needs no setup to understand. Shared as a meme sound, it works anywhere someone is single mindedly chasing something small.