burst (one's) bubble
To bring one 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! Sorry to burst your bubble, Janet, but Sarah only went out on a date with you to make Suzie jealous. A: "Come on, man, don't burst my bubble." B: "I'm sorry, but there's no way Mom and Dad will let you stay out till 11 PM on a school night."
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