It depends on what is causing my loss of motivation. Usually, it's not the project itself, but some external factor... something else going on in my life that affects my mood or thinking. But, sometimes it is actually the project. Something complex within it. Something feature request that doesn't quite "fit" or has implications that are challenging to reconcile. In that case, I will either work on something else, or I will do something else, completely unrelated to coding and let my mind work through the issue. On a rare occasion, I'll take a little time off to "refuel". There IS such a thing as coder's block, unfortunately.