Wall Street charges $500,000 for probability. an IIT professor put the real thing on YouTube for nothing over a decade ago. 160,000 people watched him define a coin flip properly. almost none of them ever traded on it. his subject is the axioms under every bet. what a probability actually is, before you dare size a position on it. every quant in 2026 is standing on this, most just skipped the lecture. Jagannathan teaches this to the IIT engineers who end up on the desks. no upsell, no thumbnail. the foundation of your whole post sits there with fewer views than a phone review. skip to where he refuses to hand-wave. he builds "the chance of heads" from the ground up, slow, rigorous, the way the people who keep the money were taught. no ticker. no hype. one chalkboard and the axioms. a quant I know says half his desk learned probability from this exact free course, not from their finance degree. you are a decade late. it is still free.