大方廣圓覺修多羅了義經略疏 2.762

2.762

未曾悟故，如人若十歲二十始盲，則眼前雖不見物，說之即能了知。若胎中無目，生來便盲，則對色之時種種為說終無所益，則先須金錍抉膜，然後指示是非。故《涅槃經》說：「如盲人不識乳色，他人為說，展轉譬喻貝、米、雪、鶴，竟不能得識其乳色。」

Because they have never awakened. For example, if a person only becomes blind at the age of ten or twenty, then although he cannot see objects before his eyes, if someone explains them to him, he can understand. But if one lacks eyes from within the womb and is blind from birth, then when facing forms, even if someone explains them to him in various ways, it will ultimately be of no benefit; one must first use a golden lancet to remove the cataract, and only then point out what is what. Therefore, the Nirvāṇa Sūtra says: 'Just as a blind person does not know the color of milk, and though others explain it to him with successive metaphors of a conch shell, rice, snow, and a crane, he is never able to know the color of milk.'