Meaning of 了如指掌

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liǎo zhǐ zhǎng
to know sth like the back of one's hand (idiom); to know (a person, a place etc) inside out
Example Sentences
But don't act as if you know everything about the place.
Probably this guy knows all about him, where he lives, and where his wife works and his kids go to school.
But do we know really know ourselves?
And at sometime in your relationship when you really know that person, you can know that it is what you want or not.
It ought to be a device that suggests things for you, because it knows so much about you.