It is also noted in classic texts: "It is useful in the early stages of an illness, but when symptoms worsen, it is of no use, because it is too gentle and lacks strength."
古籍上也記載，燕窩「病勢初淺者為宜，若陰火方盛，血逆上奔，雖用無濟，以其出柔無剛毅之力」。