When I was much younger, I was fascinated by cold-readings. I didn't want to be Watson, I wanted to be Sherlock Holmes. The idea of being able to study someone and make deductions from dress, mannerisms, speech, etc...was irresistible. In fact, I became quite good at it. And then I saw how it could be taken a step further; using that information to actually influence someone else. Suggestion is a powerful thing.
I suppose writers do this to a degree. We study people, try to imprint their behavior and language in our mind, and then make deductions about their motivations or inner turmoil. And we transfer this to paper, inviting the reader to follow our thought process, inviting them to arrive at the same conclusions which we did, and sometimes we invite them to form their own from the evidence we present. And like the onstage mentalist, we try our hand at suggestion, re-directing the reader with description, or pacing, or minor characters, as we are manipulating their emotions and laying subliminal clues through foreshadowing so that when something is revealed there is a satisfactory emotional impact.
All writers--all good ones--are mentalists.