It was a baptism of fire.

Meaning

A difficult or challenging experience that is also a learning experience.

Examples

• John: How was your first week in the new role?
• Alice: <b>It was a baptism of fire</b>! So much to learn.
• John: I figured it would be challenging.
• Alice: It was, but I'm learning a lot. It was definitely <b>a baptism of fire</b>.