[Veserv]

Every abstraction leaks. A good abstraction for your domain is stable in your domain and only leaks outside of your domain. A great abstraction is separable allowing you to only drop down the abstraction level where needed and allowing the rest of the code to continue using the abstraction where the leaks do not matter, and layered allowing you to only drop down as much as needed and making it easy to rebuild parts of the upper layers on a new foundation.