Heretical-but-deliberate Rails advice from Bellware's talk: rename `app/models` to `app/data` and do nothing with those classes beyond scaffold-generating them. Don't add validations, callbacks, or business methods. Every extra method on a highly afferent model class increases surface area — 'like Velcro' — for unrelated code to stick to, driving up afferent coupling. Keep model classes exactly as Rails generates them and move logic into `lib/`.