事后诸葛亮 (shìhòu Zhūgě Liàng) is a common saying meaning 'hindsight is 20/20.' Zhuge Liang (
诸葛亮) was the legendary strategist from the Three Kingdoms period, famous for his brilliant foresight. Being a 'Zhuge Liang after the fact' means it's easy to be wise when looking back.