I feel like the end goal has always been the incentive for me. I learned to build a PC because, if I wanted to play the games I wanted, there wasn't another option. I still do always enjoy the process of putting it all together, but I'm always ready to have it all working, booted, and put to use (if not just so I can be relieved that I don't need to RMA anything, hah).

If the end goal isn't something that interests you, then maybe it's just not worth doing it.