When I started to program, my programs would grow in length, until I hit what I called the wall. That was when my code was so complicated that it was easier to start from scratch than it was to make any modification.
Unmaintainable.
When I got some formal training, the most important thing I learned was the method called Structured Programming.
This moved the wall much further away.
Another thing I've learned over the years is not to be a snob about languages, they're all equivalent. Any program you write in one language, you can write in another.