I learned I'm more capable than I imagined. I was a mediocre student through HS and undergrad, and managed to talk my way into a really good PhD program I started this fall. All the other students were stellar students and just seemed so much more qualified, and I really doubted if I could make it.
I did well enough in my fall classes (hardest math I've ever taken, skipping multiple pre reqs) to move on and I feel I've found my research interest at least for now. I'm excited every day to work on my research/coding and honestly am 100x happier than I was at my old job even though I'm working about 5x the hours.
I was really worried from the get-go I would not be able to pass the hard classes. But shit, I did it! I feel I can just do so much more.
Sorry for the ramble haha.