Your question is Explain Design Rationale Clearly. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You're in a technical interview and have just walked through a design or implementation choice. The interviewer wants to understand not only what you chose, but why you chose it and how you weighed alternatives.
How would you explain your design rationale in a technical interview?