See but this is all about how Cersei doesn’t get it. She’s had power and privilege for most of her life, by virtue of being born to the richest family in Westeros and marrying into the royal house. Getting her own way is as natural as breathing.

Littlefinger (the guy claiming that knowledge is power), on the other hand, started out in a crappy position and ascended to a position in the royal court. He knows exactly how power works and exactly how to fuck everything up with the minimum amount of effort. 

Basically, though Cersei can threaten people as much as she wants, ultimately she doesn’t grasp the intricacies of power as much as LIttlefinger does, which is going to come back to bite her at some point in the future.