“put your finger on it”别理解成“把手指放上去”，真实含义是确切地指出。

【例句】
There's something odd about him, but I can't quite put my finger on it.
他有点儿不对劲，但我不能确切地指出。

Never put your finger on someone's faults unless it is part of a helping hand.
从来不要确切指出别人的错误，除非是为助人一臂之力。