Why did the nuclear dominoes stop in Afghanistan? This paper is a logical analysis of this question. Nuclear dominoes are common in rival relations characterized by geographic proximity, ongoing military conflict, and mutual hostility. The U.S.- USSR-China-India-Pakistan cascade of nuclear weapons development is empirical evidence of this phenomenon. However, despite the development of nuclear weapons by its arch-enemy Pakistan, Afghanistan did not proliferate in response. This study identifies and validates the reasons why Afghanistan did not (or could not) develop nuclear weapons, categorized into threat, capability, and constraint factors. The most significant finding is that Afghanistan did not perceive Pakistan’s nukes as a threat in terms of intention. Of course, it is also possible to argue that Afghanistan lacked the capacity to bear the various costs of developing nuclear weapons and that structural constraints imposed by international nonproliferation commitments, great power coercion, and regional balance of power dynamics prevented it from doing so. However, the root cause was the symbiotic relationship between the Taliban regime and Pakistan, temporarily easing the enduring rivalry, resulting in a bias in threat perception. These findings are consistent with the constructivist view of the importance of “shared understanding” in threat perception and challenge the realist perception that nuclear dominoes are inevitable in rivalry relationships. They are also significant because they provide clues for peace and stability in East Asia, one of the regions most likely to experience nuclear dominoes.