In English, “It’s not every day (that) S+V” is often used to emphasize something uncommon or a special situation.
Literally, it means “this does not happen every day,” but in actual use it carries the nuance of “it is rare” or “it is special.”
It is a natural expression that Americans use in everyday conversation with a sense of admiration, or in academic contexts when emphasizing a rare and important event.

3 example sentences for everyday conversation
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Meeting such a famous actor in person is not an everyday occurrence. → It’s not every day that you meet such a famous actor.
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Someone giving you a surprise trip for your birthday is not an everyday thing. → It’s not every day that someone gives you a surprise trip for your birthday.
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My name appearing on the front page of a newspaper is truly a special experience. → It’s not every day that your name appears on the front page of a newspaper.
3 example sentences for academic/professional English
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It is a rare opportunity for experts from such diverse fields to gather in one place. → It’s not every day that experts from such diverse fields gather in one place.
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It is uncommon for a new treatment to show such significant results in clinical trials.→ It’s not every day that a new treatment shows such significant results in clinical trials.
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Research with such a major impact both academically and socially does not come along often. → It’s not every day that a study has such a profound impact both academically and socially.