Doctors are human too. Medical error is pretty common. It's not just doctors, either; every healthcare professional is affected.

Recognizing this fact led to studies in patient safety.

https://www.ncbi.nlm.nih.gov/books/NBK2673/

It's a really interesting read, especially the chapter "Basic Concepts in Patient Safety".

I find it notable that greater safety is achieved by avoiding reliance on memory. The amount of memorization in medicine is astounding. When I tell my friends there's no shame in looking something up, they look at me like I'm some kind of madman. "What will the patient think? If you can just look something up, why have doctors at all?" Yet this article clearly advocates the use of checklists to make sure nothing is forgotten.