read (one) like an open book

read (one) like an open book

To easily analyze and thoroughly understand one, especially one's emotions, motivations, etc. I can read you like an open book, and I can tell that something's wrong, so please tell me what it is. I tried to hide how sad I felt while I was in front of my parents, but they read me like an open book.
See also: book, like, open, read
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

to

little/no purpose
With few or no results.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.