The biggest challenges for me as an intern were reading and understanding someone else's code (Python) and understanding the problem domain quickly and sufficiently. It's hard to judge how deeply you need to understand something before you program around its concepts. Of course ideally you're an expert, but when you're potentially only using something for the summer it makes sense to somehow seek an understanding of the salient concepts without getting overwhelmed by details even though it's sometimes the little caveats that can make a tremendous positive or negative difference in your design depending on your knowledge of them.

And I'll admit that self-discipline was sometimes an issue. When you take responsibility for a complex project when young and inexperienced, you feel a lot of pressure to perform and get it working so you can tackle the next task. Maybe us noobs aren't used to this sort of pressure?

I had the chance to do a code review with a few of the top engineers in the company, and it was tremendously helpful. We focused on a small part of the code that was responsible for a performance bottleneck, and I didn't realize how sloppy some of my code was until we walked through the function. There were really silly redundant things that I thought I would never have written in my right mind. I was trying to optimize a function where some of the simplest code was redundant and actually contributing a bit to the performance problem. They were nice about it and said it was not unusual and that code reviews are great for spotting such things.