Regarding the breaking of their relationship, it has been said from olden times: Kukai refused Saicho's request to borrow Rishishakukyo (commentaries of 'Rishu-kyo' [Principle of Wisdom Sutra]) and Taihan, who had been a discipline of Saicho, became a discipline of Kukai.
なお二人の訣別に関しては、古くから最澄からの理趣釈経（「理趣経」の注釈書）の借覧要請を空海が拒絶したことや、最澄の弟子泰範が空海の下へ走った問題があげられる。