Suppose the utility loss from taking a job is X, and U(income) is a concave function. Both of these are standard assumptions, well validated empirically.
With no basic income, people will take a job if U(job income) - X > U(income=0), or equivalently U(job income)-U(income=0) > X.
With a basic income, people take a job if U(job income + basic income) - U(basic income) > X.
By concavity, there are values of X for which the former inequality holds and the latter does not. So people falling into this regime will be deterred from taking a job by a basic income.
Society as a whole is poorer as a result by an amount equal to those individual's marginal productivity. I.e., fewer nails are manicured, fewer homes are cleaned, fewer restaurant meals are supplied.
Note that you can alleviate these negative effects by replacing a basic income guarantee with a basic job guarantee (i.e., just like a basic income, but you need to work for it). That also costs the taxpayer far less.