Many people would be surprised how many homeless people have (hard science) degrees or used to be very succesful. Bad luck, medical debt, (mental-)health issues, company goes bankrupt due to circumstances beyond your control, etc.

The world isn't fair. You can work really hard, and end up in the oven of a concentration camp, despite what the slogan above the gate said.

Of course, if you're a relatively talentless hack who's won the equivalent of the lottery despite not really deserving it that much, it's nicer to think that you deserve it because of your inate talent. Vanity. It's the Devil's favourite sin.