俱舍論疏 24.126

24.126

論「不爾至失正學故」，釋也。有二因：一未如實見故者，四善根中雖見諦理，不如實見，不分明故；二忍位已前容退失故。

The Śāstra says: "It is not so […] losing correct training." This explains it. There are two reasons: first, because they have not seen as it truly is—although they see the truth principles within the four wholesome roots, they do not see them as they truly are, because they are not distinct; second, because prior to the stage of patience, they are still subject to regression.