The projects I enjoy most are the ones where something gets built from nothing, and the ones with harder infrastructure and scaling problems. The second goes back a long way: I came to software through Linux, servers and networking as a teenager, and at university I worked on high-performance computing and at Selfnet, the student-run ISP for the dorms in Stuttgart. I still run my own infrastructure.
I co-founded Pocketvillage, became Head of Technology at resmio, and spent six and a half years at Lateral leading the backend and infrastructure team, next to a hands-on CTO. All three products went from no revenue to paying customers while I was there, and two of the companies were later acquired. I hired most of the engineers I led.
The impact I notice most from those years is in people rather than code: running into developers I mentored as juniors, years later, and seeing how they've grown.
Many of the people I work with don't have a technical background, so a good part of the job is written down: what we are building, what it will cost, and which trade-offs I made and why. I write the code as well.