Lesson
White to move. Main line: 1. Nc6+ Kf8 2. Nxb8
The knight on e5 masks the rook on e1. So 1.Nc6+ discovers the rook’s check down the e-file and, at the same time, attacks the queen on b8. Black must answer the check first — the king moves — and then 2.Nxb8 collects the queen.
Because the check comes from the rook, the knight is untouchable: the opponent has no time to deal with it. A discovered check that also forks the queen is one of the most decisive tactics there is.