Ornament of the Sutra Collection ཐེག་པ་ཆེན་པོ་མདོ་སྡེའི་རྒྱན།

The nature of suffering and concepts:
The suffering that all beings experience is due to not being able to realize the ultimate truth, they cling to suffering as being real.
On the second level suffering is explained to be like a dream.
On the level of the bodhisattvas it is direct realization of non-self.