But, if you’re learning HTTP status codes, or headers and auth works? That knowledge stays relevant a lot longer, and is part of all web apps. As a bonus, learning more fundamental knowledge gives you an edge when it comes to debugging problems, which is one thing that can help you stand out in your early years. Also, different types of knowledge have different acquisition costs. Basic JS or HTML is relatively easy compared to writing a full stack web app, which is easier than building a reasonably full scripting language, which, in turn, is easier than building a production grade data store like Postgresql or MongoDB.