Semel emissum volat irrevocabile verbum.
(Horace, Epistulae 1.18.71

(Pron = seh-mehl ay-miss-soom wo-laht ihr-reh-woh-kah-bih-leh wehr-boom)

Once a word has been sent flying out, it can not be called back.

Comment: The full line of this saying from Horace is that he avoids the
talkative nosy person who, even with ears wide open is incapable of retaining
or keeping secret what has been said to him, and therefore, once a word has
been sent out to him, it cannot be called back. In even more context, Horace
is offering advice, saying: watch out to whom and about what you speak.

This is really very good, very practical advice. In my own life, and then
repeatedly with my own children and students, the perennial lesson comes up for
review: if something is important to keep to yourself, then you really cannot
tell it to anyone. Invariably in schools or other communities, when an
important piece of information becomes fodder for the rumor mill, it is because
the source only told his/her “best friend” who promised not to tell anyone. And
often enough with some individuals, this happens over and over again.

Why don’t we learn this lesson? I think it has something to do with the
momentary thrill of being the one with a secret that we get hooked on. The
sobering reality is found in Horace’s words: once that word is sent flying,
once the secret is told, it cannot be called back.