That’ll be the day = That probably won’t happen.
You can use the common expression, “That’ll be the day” when you believe that something will not happen. Responding with “That’ll be the day”, is a way to express disbelief. You are saying that you think something is unlikely to happen.
Read the dialog and take the quiz below to test your comprehension:
Valerie: I think we may have to drive to the city this afternoon.
Marcus: Maybe there won’t be a lot of traffic today.
Valerie: That’ll be the day. Let’s take the train instead.
Marcus: You’re right. That might be a better idea.
Talk about it: Tell someone you don’t think that a situation is likely. Say, “That’ll be the day.” Keep getting better at English by taking unlimited live classes with American teachers available around the clock.
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