Which of the SOLID principles do you believe are the most critical for developing quality code?

All SOLID principles are important for creating quality, maintainable, and extendable code, but the most critical are:

• Single Responsibility Principle (SRP) — the principle of single responsibility. Each class or module should have only one reason to change. This simplifies understanding and maintaining the code.

• Open/Closed Principle (OCP) — open for extension and closed for modification. The code should be designed so that new functionality can be added without changing existing code, reducing the risk of errors.

These two principles lay the foundation for flexible architecture. The other principles (Liskov Substitution, Interface Segregation, Dependency Inversion) are also important, but their application often follows from correctly following SRP and OCP.