It was a wake-up call.

Meaning

An experience that alerts someone to a problem or danger.

Examples

• John: Did you learn anything from your recent mistakes?
• Alice: Absolutely! It was a harsh lesson, but <b>it was a wake-up call</b>.
• John: Glad you learned from it. How will you avoid such situation in the future?
• Alice: By being more cautious and prepared. <b>It was a wake-up call</b> that I needed to change my strategies.