To be an eye-opener

Idiom: "to be an eye-opener"

Example: 

Darryl and John are talking...

Darryl: Did you know that the average household in California uses more than 350 gallons of water a day? That's over 1325 liters everyday! 

John: Each house?! That's a real eye-opener!

Meaning: An eye-opener is a shocking or surprising piece of news. It's something unexpected that makes you think differently about a situation or about the world.

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