Writing a computer graphics engine during university taught me a couple:

1. I can use math, intuitively, even if I don't know how the exact calculation works.

2. I can use a debugger and replay it again and again to understand what's happening.

3. I can diagram a high level design and not have the complete context in mind and still produce a 10K LoC OpenGL powered computer graphics engine.

After that project, programming never felt impossible to me anymore. After that project, I always had some confidence of being able to learn whatever I needed, as long as I have enough time.

Here is the engine (2013): https://www.youtube.com/watch?v=PH6-dLvZEiA&t=1s&ab_channel=...