I'll also argue that "improving their standard of living" does not have to be separate from an expansion in the economy. Often the means these irresponsible financial stewards take in "improving their standard of living" is in spending on goods and services, which continues to contribute to liquidity in the market. Not to mention that improving the standard of living for consumers is generally an overall win for society as a whole (lower crime, lower healthcare costs, higher productivity, etc.)
If everyone gets a few thousand dollars and runs out and spends it on beer and pizza, at least they got some beer and pizza. And then the money ends up back in the hands of the people who had it originally.
There are worse ways for a project to fail, and of course all the benefits discussed elsewhere could happen.
Folks would leave stressful jobs or jobs that require you to work long hours.
One of the reasons why UBI appeals to the HN crowd is because the HN audience leans towards entrepreneurs and wannabe entrepreneurs. But for the economy at large, far more people would rather try to keep their heads down and get home to their families.
Most people are not responsible financial stewards. They don't take their excess income and put it into investments, they take their excess income and put it into improving their standard of living. That means using the extra income generated from a day-job goes to higher rent, car payments, and other liabilities not easily released.
Most middle-income people will end up in the same place - unable to leave their jobs due to the difficulty of finding a new one. Upper-income people will pay more in taxes essentially to end financial insecurity among lower-income people living paycheck-to-paycheck.