1) Computer Science theory and concepts. I might know some buzzwords but I didnt initially understand things in depth. It took time working on projects to start grasping them.
2) Perspective on the industry. People get so caught up in language and framework wars. It's easy to just take someone's opinion and run with it. After a while you realize that there isn't really a right or wrong and focus on learning underlying concepts.
3) How to keep cool under sudden pressure. Releasing a bug into prod would scare the hell out of me. Sure, it's never a good thing, but even Apple releases bugs. Taking a second to breathe and calm down can make a huge difference in effectively tackling pop-up issues.
I'm sure I'm missing some but those are the ones that came to mind for me anyways.