Similarly a Ksatriya has symptoms—a tendency for ruling over others, martial spirited, charitable, does not flee away from the battlefield and so on. Similarly, the symptoms of a Vaisya is his tendency to agriculture, trade, cow protection and banking. And the Sudra's tendency is to some way or other work anywhere and get some wages.
So Narada Muni says that these symptoms are not stereotyped or stagnant; they are flexible. A man may be born in the family of a Brahmana but he might have the tendency of a Ksatriya or Vaisya or Sudra. Similarly a man may be born in the family of a Sudra or Candala but he may have the tendencies for a Brahmana. Just like Ekalavya was born in a Candala family but he had the tendency of a Ksatriya. Similarly Visvamitra Muni was born in a family of Ksatriyas but his tendency was of becoming a Brahmana.
So Narada Muni says that men should be judged by his tendencies, not by his birth, and this is also confirmed in Bhagavad-gita by Lord Krishna that the four divisions of human society should be judged by the qualities in actual work.