I'd suggest looking at retirement- one of the important facets of retirement is the encouragement to continue contributing to society once retired because it is always necessary to be productive in some way or form for the human condition as we understand it. It is psychologically damaging to not be constantly doing stuff that is at least mildly fulfilling in some way. If a sizeable portion or even a majority of people recieved UBI we would quickly learn as a population what's always been advised to our elderly.