The Plaza Accord worked through two channels simultaneously: signal and action.
On signal: when five of the world's largest economies announce they will coordinate to sell dollars, markets have to price that credibility. Currency traders who were long dollars suddenly faced five central banks willing to sustain pressure in the same direction. The announcement alone moved markets.
On action: the central banks sold dollars simultaneously. The coordination mattered because a single central bank selling into market momentum can be overwhelmed. Five operating together cannot.
USD/JPY moved from 240 yen per dollar in early 1985 to roughly 120 by 1988 — a 50 percent appreciation of the yen in three years. The U.S. trade deficit did narrow, but with an 18-month lag. Economists call this the J-curve effect: the balance worsens before it improves because existing contracts reprice before trade volumes shift.
The intervention hit its price target. The question was what Japan had to do to get there.