burst (one's) bubble
To bring someone back to reality, especially if they are dreaming or fantasizing about something unrealistic. Look, I hate to burst your bubble, but there is no way you're getting into Harvard! You're a C student!
burst someone's bubble
If someone or something bursts your bubble, they stop you being so happy or satisfied. A terrible defeat in Saturday's match burst their bubble. Costa burst her bubble, telling her that her boyfriend had been arrested.
burst someone's bubble
shatter someone's illusions about something or destroy their sense of well-being.