White sees that the queens are faced off against each other and that Black’s queen (like his own) is protected only by a piece—the knight on c6. White has no way to capture the knight, and the knight has protection; so if White merely attacks it with a move like Bb5, Black is free to preempt White’s plans with a forcing move of his own: QxQ+. White needs a way to attack the knight while controlling the initiative. He examines other ways of going after it, and he examines any checks he can give; either way he is drawn to Ne7+, forking Black’s knight and king. Black must save his king either by moving it or by taking White’s knight. If he takes the knight with NxN, he leaves his queen loose and allows White to play QxQ. If he moves his king to b8 or d8, now what? Keep looking for the next check; especially when your knight is creating havoc and forcing the enemy king to move around, successive knight moves often can create successive checks and forks. White thus plays NxN+, this time forking Black’s king and queen. Again Black must either move his king or (better) take White’s knight. Either way his queen is loose and ends up lost next move.