I learned how a kernel actually loads a program and switches between them by using timer interrupts and interrupt vectors that point to specific locations in memory to resume execution from. Not specifically Linux related, but I'm trying to learn more computer science, and it just clicked for me two weeks ago. I've been programming microcontrollers for ten years, but those are monolithic programs, and while I knew what interrupts were and have used them, I never understood how an OS actually runs multiple things while staying in control. Now I do. About time I understood a core concept of these machines that have been here all 42 years of my life.

It's one of those "aha!" moments like when I realized classes and structs are just data types like any other in C++ when I was starting off programming and can be used like them. OOP became fun after that.