His children, who have normal hearing, don't sign, restricting his communication with them to just a few words. Their inability to just "talk" puts distance between them, giving rise to a sadness that people with normal hearing may find difficult to grasp.
由於聽力正常的子女不會手語，只能憑幾個單字溝通，親子間無法交談，形成一種「隱性隔離」，這種遺憾是一般人難以理解的。