Everyone knows that understanding an engine is necessary for employment, but I think what that "understanding" actually means is quite abstract. This lecture explains the principles of how commercial game engines operate. It creates a game loop using concepts used in Unreal Engine (Actor, Level) and provides detailed explanations of RTTI concepts, which allow for a custom approach to downcasting. Additionally, when looking at Unreal Engine code, I didn't really know what the `ProjectName_API` prefix before class names was for, but after taking this lecture, I learned it is for using DLLs. I also gained a detailed understanding of the concept of separating engine code from content code.