Keep calm and carry on

North Korea's recent missile tests suggest that isolated country is rapidly developing the ability to deliver a nuclear weapon to the west coast of the United States, if it hasn't already. That is indeed a scary prospect. But Zócalo columnist Joe Mathews says our reaction should not be panic or despair. That would only reward Kim Jong Un's belligerence. Instead, we should take a page from the South Korean playbook, where the populace is surprisingly calm in the face of the North Korean nuclear menace. Mathews says the best we can hope for is to be prepared and stay cool.