Older meaning of propriety?

I have a question about the meaning of the word propriety before the Victorian age:

"As it is most frequently used in Pride and Preludice, "propriety"
suggests a kind of behaviour which is particularly careful not to violate
the privacy, the integrity, and the right to respectability of every indi-
vidual. As a concept governing social relations, then, "propriety" is
intimately concerned with the discretion and reserve necessary to pre-
vent individuals or actions from becoming "common" through exces-
sive familiarity"

I don't understand the underlined part..Can anybody elucidate this, maybe with an example?

Thanks a lot!