Easily has to be thinking that having credit is financial freedom. Repeatedly in his life he was paying for trips credit cards (for street fighter), taking thousands out in cash advance on credit cards (to pay out money matches from credit cards), paying for bills on credit cards because he overextended himself buying statues, funding a move across the country on credit cards, then opening more to furnish the house on credit cards. It's the same mistake repeatedly. A clip we all know is him talking about how 2014 right after moving to Washington was the last time he had "financial freedom" by which he doesn't mean what we all take it to mean, but instead that he was spending freely. He means quite literally the opposite of the term. Now he looks forward to when he can take out a loan against his own mortgage to do who knows what with and get credit cards again as when he will gain financial freedom again. He's made this remark repeatedly.
His worst financial mistake was never understanding personal finance at all, period.