Don't be too hard on yourself. I'd be a little freaked out if you were good at everything the first time - and your brilliance scares me enough as it is :)

The title of your post says it all - it's about what you learnt from it. You don't learn anything if you get it right the first time. From now on you'll be paranoid about doing the obvious things and it'll be good for you as a doctor. Sometimes it's the simple things that people become complacent about. It'll all seem easy to you after a while.

Good luck with it all Frey!