观机而动 (觀機而動) guān jī ér dòng

guān jī ér dòng set phrase observe an opportunity and then act
Domain: Idiom 成语 , Subdomain: , Concept:
Notes: 观 in the sense of 观察, 机 in the sense of 时机, and 动 in the sense of 行动 (Guoyu '觀機而動')