Lesson
White to move. Main line: 1. d7+ Kb8 2. c7+ Ka7 3. d8=Q
The pawns advance with tempo. First d7+ forces the king away from c8; then c7+ takes over the checking duty and drives it farther from the d-pawn’s promotion square.
Connected pawns protect each other diagonally, so the king cannot simply capture the rear pawn. Once both stand on the sixth rank, advancing one while the other guards it creates a compact mechanism that a lone king often cannot stop.
The practical rule is to avoid pushing both automatically. Start with the pawn whose advance gains a tempo or denies the king its best blockade. Here the checks fix the move order and leave d8 clear for promotion while the c-pawn controls b8.