It was a real eye-opener.

Meaning

It was a surprising and insightful experience.

Examples

• John: How was your trip to the Amazon rainforest?
• Alice: It was amazing! <b>It was a real eye-opener</b>, seeing how different life can be.
• John: In what way?
• Alice: The scale of the ecosystem, the challenges faced by the locals... <b>It was a real eye-opener.</b>