The simple form again, this time running vertically. The kernel of the discovery should be evident on the e-file. White sees that the king is at the other end of it and thus realizes that his knight will have a free move. Black’s queen always is a favored target; here it’s on a light square, as is the knight, so it can be reached the move after next. 1. Nc5+, Kf8; 2. NxQ wins the queen for the knight.