瑜伽師地論略纂 4.111

4.111

行有三問答。初、「由不了達世俗苦因為緣，起非福行」等者，三惡趣苦，相狀易知，名世俗苦；人天趣苦，微隱難了，聖智所知，名勝義苦。

On volitional action, there are three questions and answers. First, regarding 'conditioned by failure to comprehend the cause of conventional suffering, non-meritorious action arises': the suffering of the three bad destinies is easy to recognize by its characteristics, so it is called conventional suffering; the suffering of human and heavenly destinies is subtle, hidden, and difficult to comprehend, known by noble wisdom, so it is called ultimate suffering.