Recently I had the experience of reviewing a project and accessing its scalability and maintainability. There were a few bad practices here and there, a few strange pieces of code with lack of meaningful comments. Nothing uncommon for a relatively big (legacy) codebase, right?
However was something that I keep finding. A pattern that repeated itself throughout this codebase and a number of other projects I've looked through.They could be all by lack of abstraction. Ultimately, this was the cause for maintenance difficulty.