It was a wake-up call.

Meaning

The experience made someone realize something important.

Examples

• John: 'Failing that exam made me realize I needed to study harder.'
• Alice: '<b>It was a wake-up call</b>, then.'
• John: 'Yes, <b>it was a wake-up call</b> for many.'
• Alice: 'Seeing the effects of pollution made me change my habits.'