I forgot another category, and that's parts and component sourcing. On bigger projects that can be quite an adventure sometimes. Solved easily with money, but not all of us have endless bank accounts, so then you have to scour the classifieds, and auctions. Do some digging for the deals, or maybe drywall a few basements along the way.
I have a few projects that are quite a few years in the making because I just buy components and material when I find them for cheap. That's a pretty enjoyable part of the process for me. It's not always about the end goal, it's the journey and the process, and eventually being able to step back and say "I made that. I designed and built that with my two hands".