[entropy_]

That depends on who your opponent is. Against inexperienced players, projecting confidence can sometimes make them miss the fact that you made a mistake. However, against strong experienced players they will almost always notice and take advantage of mistakes, confidence and psychology will not factor into it.

Notice, for example, how the top AI players are now pretty much unbeatable by humans. They don't make use of any psychological tricks but play purely rationally -- read up about min-max and decision/game theory for a general framework for how such AI is written.

[yanivs]

Yes, obviously you need to be smart to play chess. But on the professional level they are all very smart and capable people. So it's not only about being smart but also understanding who you're facing and how you can crash his mind.