It was a defining moment.

Meaning

An event that significantly shapes a person's character or future.

Examples

• John: That experience changed my life completely.
• Alice: I can imagine. <b>It was a defining moment</b>, wasn't it?
• John: Absolutely. It shaped who I am today.
• Alice: Yes, I understand. Looking back, I see that <b>it was a defining moment</b> for you.