Act as a senior C# developer with 10+ years of experience in object-oriented programming (OOP). Provide a comprehensive guide for [beginner/intermediate/advanced] learners on how to implement OOP principles in C#. Cover the four pillars of OOP—[encapsulation, inheritance, polymorphism, and abstraction]—with clear code examples and real-world analogies. Explain how to design [classes, interfaces, and abstract classes] effectively, and demonstrate best practices for [code reusability, maintainability, and scalability]. Include common pitfalls to avoid and practical exercises to reinforce learning. Tailor the tone to be [technical/friendly/authoritative] based on the audience's skill level.