(Ichidan kin ni hisha sute ari)
Vacabulary: ichidan=the first (bottom) rank, kin=Gold, ni=in (...ni ari=exist in...), hisha=Rook, sute=throwing away
(1) When your camp is well-protected against a Rook drop, you can sacrifice your Rook. This is what the proverb teaches.
White in hand: R 9 8 7 6 5 4 3 2 1 +---------------------------+ | * * * * * * * * * |a | * * * * * * * * * |b | * * * * * * * * * |c | * * * * * * * * * |d | * * * * * * * * * |e |bP * bP * bP * bP * bP |f | * bP * bP * bP * bP * |g | * * bK bG * * bS * * |h |bL bN * * * bG * bN bL |i +---------------------------+ Black in hand: nothing Diagram 1.When a Gold is on the first rank as in Diagram 1, there's no room for a Rook drop. The combination of the Silver on 3h and the Gold on 4i makes a strong defense against a Rook drop.
A Silver on the first rank, in contrast, makes an ill-shaped defense.
Diagram 2 shows where a Silver and two Golds are placed around the King, building up a sturdy guard. On the other hand, the right side of the camp is weaker.
White in hand: R 9 8 7 6 5 4 3 2 1 +---------------------------+ | * * * * * * * * * |a | * * * * * * * * * |b | * * * * * * * * * |c | * * * * * * * * * |d | * * * * * * * * * |e |bP * bP * bP * bP * bP |f | * bP bS bP * bP * bP * |g | * * bK bG bG * * * * |h |bL bN * * * * * bN bL |i +---------------------------+ Black in hand: nothing Diagram 2.White will drop the Rook on 3i.
Provided the opponent has a Rook in hand, your King is safer in Diagram 1 than Diagram 2. This is one of those ironies in shogi that you should keep in mind: A seemingly sturdy castle with Silvers and/or Golds closely around the King can invite a dangerous Rook drop.
(2)
White in hand: P 9 8 7 6 5 4 3 2 1 +---------------------------+ |wL wN * * * wG * wN wL |a | * wR * * * * wK wB * |b |wP * * * * wP wS wP * |c | * * wP wG wP * wP * wP |d | * wP * wP * bS * * * |e | * * bP * * * * * * |f |bP bP bB wS * bP bP bP bP |g | * * * * * * bS bK * |h |bL bN * bG bR bG * bN bL |i +---------------------------+ Black in hand: P Diagram 1. Up to ....S*6gDiagram 1 is from an actual game where White has just dropped a Silver on 6g. Black wants to play Sx5d, but White will respond with P*5f thereby closing up the Rook's path. How would you play here?
Rx5d
Black has two Golds on the first rank, which is a strong defense against a Rook drop. So, Black resorted to an aggressive move: Rx5d. This made White's Silver on 6g look pointless, since the Silver was intended to restrict Black's Rook.
Moves thereafter: ..... Gx5d Sx5d B-1c P*6d (Diagram 2) White in hand: R P 9 8 7 6 5 4 3 2 1 +---------------------------+ |wL wN * * * wG * wN wL |a | * wR * * * * wK * * |b |wP * * * * wP wS wP wB |c | * * wP bP bS * wP * wP |d | * wP * wP * * * * * |e | * * bP * * * * * * |f |bP bP bB wS * bP bP bP bP |g | * * * * * * bS bK * |h |bL bN * bG * bG * bN bL |i +---------------------------+ Black in hand: G P Diagram 2. Up to P*6dBlack's Silver is now edging up on White's King, while White's Bishop and Silver on 6g are idle pieces. The position above is in Black's favor in spite of Black's material loss (a Gold for a Rook).
Take note that White's B-1c was a good move in his bad position, placing the Bishop on a better square and giving the King more breathing space. However, Black's next move, P*6d, was even better, gaining ground for further attack.
A Rook is a strong piece and you may well be reluctant to let it fall into your opponent's hand, but provided your camp has no hole for a Rook drop, the sacrifice of it is certainly a possibility to be considered.