This. I can do programming problems in Java, but I definitely can't lead a team doing a Java project. I don't what Gradle/Maven/etc really are. I don't have years of experience with how libraries, the API request pipeline, middleware, etc work. I don't know little tricks / nuanaces, like the fact that Visual Studio has to be restarted for local code to pick up new environment variables, why String and string are the same thing, etc, etc, etc.