Hmm. off the topic of my head I learned a few things -
1) it made me realize that while it's useful to have a long term plan, it's important to be flexible. I started off with a simple premise and with no real plan. Made an outline for the story early on while writing. As I went along, I had other ideas from random bursts of inspiration and changed my story along the way/edited my outline as needed based on how I felt the story was going.
2) My definition of goals changed as I went along with it. Rather than "I want to finish this novel," I realized during the process that having smaller goals and working through them ("I will write one chapter by the end of the week" or "Yes, I'm tired of writing this part but I'm going to write this scene ahead that I'm excited for") was a great way to stay motivated.
3) It's important to me to set aside time for myself to do things I enjoy doing, self-care is important, and this was a huge coping strategy from other academic work
4) This experience of writing taught me a lot about how I deal with being 'stuck' (Sometimes I had no idea how to progress despite having a plan, and nothing I wrote sounded right. I liked to read and take walks for inspiration)
5) It was really nice to actually finish. quarantine definitely helped speed it up LOL but being able to see end, tangible results was incredibly rewarding and i felt very proud that I stuck with it despite moments of waning motivation