The Hanoi talks ended in deadlock. Both sides – represented by U.S. President Donald Trump and North Korean leader Kim Jong Un – showed their anger by refusing to shake hands. The media labeled the talks a failure. But I've been involved in a number of negotiations in my life, and I see this as a normal part of the process. At some point, all parties will take positions designed to test the other side's hunger for a deal, and prudent negotiators know that showing hunger can be devastating. So, ending the negotiation, particularly with a show of anger, is routine. At the same time, mutual rejection can be genuine, and now each side is trying to figure out how serious the other is. Establishing that you are prepared to walk away from the table is important – but sometimes the deal falls apart as a result.