1. attempt to understand how somebody thinks
Professional
Social
get into the criminal's head
The idiom to 'get into somebody's head' means to make an attempt to understand how someone thinks or how they are feeling usually because you want to manipulate someone or catch them out in some way.
2. attempt to disrupt someone's focus, performance, or confidence
Professional
Social
don't let the opposition get into your head
often in order to manipulate or undermine somebody