For those of us with work ethic (the vast majority of everyone, to varying extents), our extra effort will be rewarded by the market, if we do something that other people find valuable, or intrinsically, if we're just doing what we love.
UBI is a very interesting concept, but in order to sell it you'd have to have a phased approach... one of the phases I think would have to include some sort of checks and balances.
While we are making recommendations about what people with issues should be doing with themselves, let me add, on the other end of the spectrum - overconfident, mindlessly ambitious characters in society, should be sent off to explore the deep sea, climb mountains etc. So that whatever random goal they are chasing has minimal impact on society at large.
I suspect most people who are in really shit jobs are there because they have issues... they can't show up on time, they don't follow employment rules, or they have something just wrong with them (they are sex-offenders, or have untreated behavioral issues or whatever)... not the sort of people who should be empowered to just sit around. I will go so far as to say nobody who really has potential ends up spinning a sign for very long... they use the job to cover their rent, and they find a way to get a better job.
Anyway I don't want to come off as against a UBI, I but I've never met someone who benefited by sitting around doing nothing. I think it's bad for people to be lazy -- like fundamentally brain-rotting to sit around being idle. I like the idea of a UBI that's tied to doing something... anything... getting outside and picking up trash in the road ditches even... or getting vocational training (which we should find a way to make free)... or getting mental health treatment... Prove you have a regular paycheck, or prove you are clocking in 30 hours at some "just move your body" type of approved activity every week to qualify.