Our speech is one of few tools we have to interact with the world, so it is wise to use it carefully.
In the past, guides of gentleman's etiquette recommended to never criticize someone behind their back, and never in public. To criticize someone in front of a crowd is likely to embarrass them, or even provoke resentment.
Therefore, criticism should be in private, and to a person’s face, in order to give them the best chance to recognize their mistake and adjust their behavior.
Gossip in general is unproductive. Talking foul of another, or talking about their affairs, is unlikely to lead us to greater truth. While we might get some pleasure from it, there are many ways to get pleasure - speaking about our own dreams, goals or even problems in a way that is enjoyable and respectful of others.
Read the transcript and find important links on the site: A Beautiful Thought - Purposeful Speech: Episode 421