Every developer remembers the excitement of writing their first application. Seeing a program finally run after hours of debugging is incredibly satisfying.

But after building a few real projects, I noticed something interesting.

Writing code that works today is easy.

Writing code that still works six months later after dozens of new features is the real challenge.

As projects grow, small design mistakes become expensive. A simple feature request suddenly requires changes in multiple files. Fixing one bug unexpectedly breaks another module. Testing becomes frustrating because everything depends on everything else.

That's exactly why the SOLID Design Principles exist.

They aren't rules to make your code more complicated.…