you can't make it through an MIT physics degree while being a total moron. Same with the Jane Street interview process. he was at least a smart guy and probably a good trader.

now in some sense you can still be very smart but "a total moron" meaning you make stupid and bad decisions and ruin your life and cause all kinds of disasters.

my read on him is he was sharp, and able to succeed for a while as long as someone else put up guardrails that would compensate for his terrible judgment and executive functioning -- which you get in school or working for a large firm. when he struck out on his own, he lost all that, but his reputation + connections + stupid risk appetite took him far until he blew up.