Another study in due care. Black has just played Nf6, resulting in a common position four moves into the open Sicilian defense. White’s e-pawn now is under attack and is not protected. White has to do something; but what? One possibility is to push the pawn to e5. This might seem attractive because it advances White’s center and attacks Black’s knight, forcing it to move. But first you need to notice that White’s d-pawn and Black’s c-pawn have been moved—a normal state of affairs in this opening. This means that Black’s queen is one move away from being able to both check the White king and attack any White pieces on the fifth rank, which White must therefore regard as a zone of great danger. Playing e4-e5 thus is a mistake because it leaves the pawn loose; it will be taken a move later by the double attack Qa5+. White should instead protect the pawn with Nc3.