Hello, Seongmin Lee. Thank you for leaving a review and congratulations on completing the course. It was challenging to prepare example code suitable for the lectures, but I'm glad the course was helpful. :) Design principles cannot be applied mechanically and can only be effective when applied in a way that suits the current situation. The best way to establish this standard is to evaluate whether the current code is suitable for changes from a design principle perspective whenever new requirements are added, and if not suitable, to think about what refactoring approach would be good and actually refactor the code. As you see the refactored code become more useful for changes and gradually improve to accommodate future changes more easily, you'll develop your own standards for applying design principles. In summary, the most effective approach is to repeatedly practice evaluating code from a design principle perspective and refactoring it to accommodate new requirements. If you get stuck or have any questions while practicing, please feel free to ask anytime! Thank you. :)