You'd be surprised how many homeless people have hard science degrees or previously ran succesful businesses. Bad luck, ill health, medical bills, a family member who needs to be taken care of, (government) corruption, fraud, theft, builders didn't fix your roof right and you're stuck with the bill and negative equity, etc.
It is possible to commit no mistakes and still lose. That is not weakness, that is life.
The idea that hard work will set you free, a slogan that historically featured above many a concentration camp gate, is a comforting lie but a lie none the less.