I believe, if you really want to understand how a game engine works, you need to try to build a game from scratch in your favorite programming language. It's a

I believe, if you really want to understand how a game engine works, you need to try to build a game from scratch in your favorite programming language. It's a fun exercise and you really grow as a programmer. If you use an existing engine, you will never really need to know how to initialize a window for rendering, you never need to touch opengl/directx/vulkan/etc, you never create a rendering loop, a scene tree, implement a matrix library, create a basic physic engine or integrate a scripting language. All those things are fun! I know it, because I spent about 8 years on and off tinkering on my own engine in my spare time when I was younger. And what can I show you after all those years? A fun tech demo maybe, but other than that, not a single finished game. Game development is different nowadays. To stand out, you need to know about game design, concept art, color theory, texturing, tile-mapping, lighting, shaders, interface design, sound design, sprite animations or skeletal animations, networking... The list goes on and on. And then your game also needs to be fun! If you go the route of implementing or integrating everything yourself, you will never reach the level of someone who knows an existing engine in-and-out. Today, if you want to create games, it's far more important to create as many games in a short time as possible. Just look at competitions like Ludum Dare to realize and appreciate how far even small game engines can help you to create a fully fledged game within 48 or 72 hours. It's crazy. This will improve your skills as a game designer far more than building your own engine.