jump跳，gun枪，jump the gun本意指“抢跑”，意思是未听发令枪就起跑，故引申为操之过急、过早行动、抢先行动。      

【例句】
You should not jump the gun in drawing the conclusion before your experiment is finished.
你不应在实验还没有做完就抢先下结论。

Don’t you think you are jumping the gun by talking about marriage so soon?
你不觉得你这么快就谈论结婚是太早了吗？