当你把幸福掌握在手中的时候,它看起来总是微不足道,但当它不见的时候,你才会了解它是多么重要和珍贵。(5月30日之每日名言)
Natural experiments are a powerful tool for understanding causal relationships in the real world.
I'm a work in progress. I'm not perfect, but I'm trying every day.