About 4 years ago, I was managing a guy right out of school who pushed a minor bug that broke real-time risk calculations for a major multinational financial institution in the middle of the European trading day, prior to the NYC open, and people were yelling over email that they were trading blind. Someone had committed an important change right after his, so a simple rollback was highly sub-optimal.
Remembering how I felt years ago, I reassured the new guy that people were yelling over email because it was important, not because they were mad at him. I told him that I thought he was the most familiar with his change and the most capable person to fix it, and that he should do his best to calm down and focus, but he should let me know if he needed help, and I would do my best to calm folks down. I told him he would probably remember that mistake the rest of his life, but nobody else was going to remember it a week later. He had the bug fix in production in under an hour.
He sent me an email from home that night worried that he had let the team down, and I reiterated that he was going to be the only one who remembered the mistake longer than a week. The post-mortem follow-up was just to reiterate to authors and reviewers the importance of corner-case tests, and nobody brought it up later.
I really only remember it because my manager sent me an email that night praising how well I handled the new guy's first big production bug.
This is outstanding advice, and very well put. I shall be borrowing it, thank you!
Edit: if you are managing someone who is new in a job, it's your job to make sure they don't push bugs to break important stuff in the first place.