How does UBI take into account mental incompetence, addictions, poor decision-making, bad luck, and bad investments, and where do you draw the line?

Don't a lot of welfare payments have strings attached, with regard to what you can spend it on? UBI explicitly does not, so you can use it for anything you want. If UBI did completely replace the social safety net, and someone gambles/fritters away their basic income and can't get a job to make more, are they allowed to starve (or depend completely on private charity)?