The 35 year mistake was the idea that in order to have a well structured program, your compile time hierarchies have to represent real world relationships.

The talk traces that mistake to Simula, where it was appropriately used, because it was intended to simulate the real world hierarchies. Then to C++ where it started to become used inappropriately, then to Java, where it became a universal Praxis to model all real world relationship as compile time hierarchies.