Ivan Nemytchenko's distinction: asking users to confirm their password or rendering a CAPTCHA checkbox is application logic (a technical detail of the web app), not business logic, yet Rails encourages putting it in the model. Domain models should not depend on the programming language, application type (web/desktop/mobile), or the framework — they should capture only the structure and functioning of the explored domain. Conflating these layers, combined with 'fat model, skinny controller', pushes framework-level concerns into the domain.