Coding is intertwined

These are also well known issues. If a software developer does not avoid these pitfalls, what happens often, is his software becomes like spaghetti. Basically, it's all intertwined, and hard to maintain, so it may work at first, but then somebody else comes in, and tries to maintain it, or tries to change it, and he will get lost, because he will not understand the code, or he will understand it, but he may not understand it completely. He may miss out certain idiosyncrasies, about the code, and when the code becomes big and bulky, you basically have to throw it away, and start all over, because it will become impossible to maintain.