A sufficiently low UBI (survival, not comfortable survival with all kinds of nice-to-haves) would be wage subsidy (or microentrepreneurship subsidy, or subsistence farming subsidy) in all but the most extreme cases of zealous frugality combined with a heavy disinclination to work. Excess money beyond survival is a very strong incentive, much stronger at least than replacing survival level welfare with survival level earning, which is what existing systems routinely expect to happen.