Introduction - Ruby Science by thoughtbot

Ruby on Rails is more than 15 years old and its community has developed a number of principles for building applications that are fast, fun and easy to change: Don’t repeat yourself, keep logic out of your views, don’t overload your controllers, and keep business logic in your models. These principles carry most applications to their first release or beyond.However, these principles only get you so far. After a few releases, most applications begin to suffer. Models become overloaded, classes become few and large, tests become slow, and changes become painful. In many applications, there comes a day when the developers realize that there’s no going back.