China’s apathetic attitude toward South Korea’s call for international efforts to reveal the truth regarding the sinking of the Korean corvette Cheonan in March 2010 bewildered many observers. Most analyses have attributed it to a problem characteristic of alliance politics; namely, fear of entrapment in a conflict between an ally and its enemies, or the defection of the ally. This article rejects such analysis as the source of China’s attitudes toward North Korea’s provocations for two reasons: The first is that China reckons the cost of entrapment would be greater than any gain—a constraint that has the opposite effect for North Korea. The other is structural, in that neither China nor North Korea can afford to abandon the alliance against the South Korea-U.S. and U.S.-Japan alliances. An abandonment strategy toward alliances is effective only if a state has a strategic option to defend itself on its own or to align with others, and if an ally can defect and/or align with others, including the adversaries of the alliance. The true motivation for China’s attitude can be found in the security dilemma posed by the situation.