
A frustrating college lecture sent David Yu into a dorm-room building spree. YouLearn grew from that impatience into an AI tutor for millions, with a harder question at its center: what makes someone come back to learn?
A college founder turned a fast-food shortcut into a product, and a lifelong fascination with water into his next experiment. The interesting part is not the variety of ideas. It is how readily he lets the weaker ones go.

At 19, he traded a French engineering-school track for a $50 Tenderloin room, an unreliable Wi-Fi connection and a Y Combinator interview. Three products later, the constant is less glamorous: Alexandre Klobb is still beside him, and each pivot begins with a problem they have felt up close.