I just pretend I’m working on something for a new hire. I don’t believe it, but really playing it up helps. If I’m alone, I’ll straight up narrate my actions to an imaginary person.
Most of the other “trick yourself” things don’t work for me though. I also can't really reward myself after doing something to incentivize it, because I tend to get so distracted thinking about the reward that I convince myself I’ll work better after having it. Worse, even if I’ve actually gotten something done, I still don’t really ever feel a sense of accomplishment.
