If you're used to Java, Elixir is like `javac`, Beam is like `java`. Mix is like a (way better) version of Gradle. You need elixir to compile your app, you only need the Beam to run it. Once you've built your project, you don't need Elixir anymore exactly like java/javac. C and rust compile to machine code so don't have a runtime dep, but otherwise they still require you to have a compiler at build time, just like elixir.