How a “defending” Queen tricks you into blundering

Advanced chess players are well acquainted with terms like “combining defence and attack”, “using multi-purpose moves”, “setting up well-hidden traps” etc. They are also familiar with the usual “advices”: Play well, Don’t blunder, Beat them all! Indeed, general principles and advices are good to guide us but then what? What a player really needs is more specific stuff. So here it is, a very well defined concept including all the above terms.

Take another look at that Qe8 move: The Queen was under attack by the Bishop on g5 and moved away to a safe square, on the 8th rank...Well, i don't know about you, but that would seem to be on the defensive side to me, and certainly not the beginning of a nasty tactical shot involving measures against a3, which even great Gelfand missed! Oh wait, Black moves Qe8? A defending-looking move with a hidden tactic? That reminds me of something...I guess i haven't learned my lesson yet but at least i hope you have!