大般涅槃經疏 14.18

14.18

第七觀求不得苦。還約前愛離冤會，於愛求會而離、於冤近離而會，二求不遂，即是求不得苦。

Seventh, contemplating the suffering of not getting what one seeks: still referring to the previous [pairs of] separation from the loved and association with the hated, one seeks association with the loved but is separated; one seeks distant separation from the hated but is brought together. When these two seekings are frustrated, that is the suffering of not getting what one seeks.