You shouldn't spoil things for others.
Trevor just saw an exciting new movie at his local cinema.
Trevor wants to talk about the movie he just saw.
Trevor refrains from talking about the movie to his friend who hasn't seen it and talks about it with a person who has seen it instead.
Trevor tells a friend who has not seen the movie all about it.
Trevor's friend enjoys the movie without knowing how it turns out before hand.
Trevor's friend feels that the movie has been ruined for them now.