strike first and gain the upper hand (idiom, martial arts term); Making the first move is an advantage.
Definitions (粵典–words.hk)
語句
要先發制人,先可以贏到人 to gain upper hand by taking the initiative; literally: one who strikes first gains the advantage;
唔好再等喇,先下手為強,行動喇。
唔好再等喇,先下手为强,行动喇。
m4 hou2 zoi3 dang2 laa3, sin1 haa6 sau2 wai4 koeng4, hang4 dung6 laa3. Do not still waiting, we have to take our first gain, let's do it.
As the saying goes: As long as you dont offend me, I dont offend you; But there's another saying: To strike frist means victory, to strike second means tragedy.