Or weak typing. How many languages thought that simplifying strings and integers and other types into "scalar", and making any operation between any operands meaningful, would simplify the language? Yet every single one ended up becoming a total mess instead.
Or constraint-based UI layout. Looks so simple, so intuitive on simple examples, yet totally failing to scale to even a dozen of basic controls. Yet the idea keeps reappearing from time to time.
Or an attempt at dependency management by making some form of symlink to another repository e.g. git modules, or CMake's FetchContent/ExternalProject? Yeah, good luck scaling that.
Maybe software engineering should have some sort of "Hall of Ideas That Definitely Don't Work", so that young people entering the field could save their time on implementing one more incarnation of an already known not good idea.