One of the Ruby on Rails fundamental principle is “convention over configuration.” It aims to reduce the number of decisions that developers need to make as it gains simplicity but not losing flexibility. The simple phrase implies that a developer only needs to indicate alternative aspects of the application. When the convention implemented by the tool you are utilizing equals your desired behavior, you take pleasure in the gains not even having to write configuration files. When your desired behavior digresses from the implemented convention, then you configure your desired behavior. The programmer can work at a higher level of abstraction with all this configuration free approach to programming.

Also known as Single Point of Truth, “don’t repeat yourself” or DRY is a process philosophy seeking to reduce duplication especially in computing. This philosophy stress on that information should not be duplicated because it makes the change more difficult, it can lessen clarity and may lead to inconsistency. DRY is from Andy Hunt’s and Dave Thomas’ principle in the book of Pragmatic Programmer. A revision of any single element of a system does not alter other logically-unrelated elements when the DRY principle is effectively applied. Moreover, elements are kept in sync because elements that are logically related all change predictably and evenly.