Single Responsibility
Domain: Design Principles
🎯 Motivation
Every class or function should have one reason to change. When code does too many things, fixing one bug can break something unrelated, making maintenance risky and confusing.
📋 Concrete Example
A User class that also sends emails violates this principle. Split it into User for data and EmailService for sending, so each can evolve independently.
🔗 Analogy
Like a Swiss army knife with 30 tools — it is hard to use any single tool well. A dedicated chef’s knife cuts better because it is designed for one purpose.