According to the explanation given in the "Jokyu ki" (Chronicle of the Jokyu Era) and other ancient sources, this resulted from the curse of "getting too big for one's breeches" (the idea that if someone rose to an official post beyond what was appropriate for them, disaster would occur); when the retired Emperor Gotoba heard of Sanetomo's death, he was inordinately pleased.
『承久記』など旧来の説では、これは「官打ち」（身分不相応な位にのぼると不幸になるという考え）などの呪詛調伏の効果であり、後鳥羽上皇は実朝の死を聞いて喜悦したとしている。