The principle
The moment of victory is often the moment of greatest peril. In the heat of success the temptation is to push further — and the overreach is what loses what victory had won.
The application
Stop one move earlier than your appetite tells you to. The last move is almost always the one that hands the position back. The discipline is to leave value on the table on purpose.
The defensive tell — how to spot it being run on you
When a counterparty in a winning position keeps demanding more after the deal is structurally settled, they are about to break the deal entirely. Decide whether to give the last inch and lock it, or walk and watch them learn this law the hard way.