The catalyst is the reversal of passive flows, specifically from target-date 401k funds. Cites Mike Green's prophecy that when flows taper and turn to outflows, it could cause a '1929 magnitude crash.'
Explicitly connects his AI job loss thesis to this catalyst: laid-off knowledge workers will stop contributing to, then withdraw from, their 401ks, triggering the outflow. States he was 'completely sanguine' five weeks ago but has now '180ed.'