1) Being unfamiliar with git. e.g. knowing that you have to fork numpy first, then clone from your fork, then create a feature branch. That's just the """straightforward bit""". It's hell the first time you have to rebase something/correct commit messages/squash, etc.

2) I have a mindblock on the correct way to use ReStructured Text in docstrings. When do I use backticks/double backticks, etc. Getting documentation changes to perfection is hard.