A lot of those "accomplishments" while they're high are placebo, and once they're sober again, they realize what lazy bums they are.
Marijuana isn't a demon plant with its roots in hell, but it's also not a miracle cure-all. I've never understood people who can't see both the pros and cons.
well accomplishments like making music, coming up with ideas, having good conversations, putting together some good food combinations, playing better at video games, and just enjoying things more are plausible, but things like going out and building a house, or having ambition to go out and find a job stoned doesn't happen. maybe they are placebo and they say it to feel better about themselves.