洞若观火（洞若觀火）　

◎ 洞若观火 dòngruòguānhuǒ

[as clearly as a blazing fire;see very clearly as through looking at fire] 形容对事物观察得清楚明白,就像看火一样

老祖台察吏安民,洞若观火。——清· 钱谦益《致郎制台》