Lesson
White to move. Main line: 1. Ra7 Rf8 2. h4
Ra7 seizes the seventh rank. From one square the rook attacks the pawn chain from behind and ties the black rook to passive defense, and that activity is worth exactly the pawn White is missing — the position is dead level.
The practical rule: put your rook where it makes threats every move, even at the cost of a pawn. A passive rook defending a pawn is often losing even with equal material; an active rook a pawn down frequently holds.
The point is the placement, not a tactic. Compare it with the passive 1. Ra2, which defends nothing in particular and leaves Black free to advance — same material, worse game.