The ones I knew working minimum wage lived cheaply. They didn't worry about losing their jobs because they were hard workers who could be counted on - the type of person who gets the maximum raise until they top out the pay scale. They were also the type of person to be offered job in management and have the potential to make as much as anyone with an engineering degree (we haven't kept in touch - typically the requirement to move for the job every few years catches up and they decide the next promotion isn't worth it and so stagnate at nice wage that is better than average)
I knew people who sit around drinking bear and working part time. Everybody knew they were losers. It wasn't lack of opportunity that is keeping them down it is lack of following up on it. They would abandon their kids even if you paid the a million dollars a year (even assuming they don't overdose on some drug)
I also know mentally ill people. Their abilities vary, but UBI won't help them as they will just waste it on some other scam. (I know someone who lost money to the Nigerian prince scam, and a dozen others - the family is careful to lock down his money now so he can't do that)