You could easily walk into my house and find the kitchen. The stove and sink are both there as expected. But despite how carefully I thought it through and built it, and despite the fact that it made perfect sense to me, I doubt you'd find my custom-built intranet app easy to navigate.

On the other hand, my last Rails app has a structure familiar to any Rails developer. The actual business logic is unique, but that's the part that has to be unique. "How do we update the database schema?" is a given.

And if it's unfamiliar, there's plenty of documentation and blog posts to help you. With custom-built code, there's no help on the web.