◇ Just read — no move neededForced means forced
弃子入局 — sacrificing into the attack — only works when the defender has no choices. The test for every sacrifice: after the piece is offered, does the opponent have a real decision, or exactly one reply? One reply per move, all the way to mate — that is 入局, entering the position for real. Two plausible defenses and you are not sacrificing, you are donating. The sacrifice usually aims at the palace: a captured advisor cannot be replaced, and the king's shrinking flight squares do the rest.