Usually, breaking things up into smaller pieces makes it easier to test the code and understand what is going on. A side-effect of breaking things into pieces is they often can be more easily reused. Unfortunately, most people don't have a knack for breaking things up into the right pieces. If you don't have a talent for it and don't invest the time and mental resources to compensate for that, yes, your attempts to create a scalable design will fail. But like any skill, you'll only get better at it if you practice. Refusing to practice means you'll be limited by your innate capability.