My trick was to find a way to obligate myself to finish. Biking to work was a huge win for my fitness. Even on days I didn't really want to bike a few more miles at the end of the day, I still had to get home.

For my kids, I'm trying to convince them that a lot of the things they find uncomfortable are things they just aren't used to. Ergonomics have fooled a lot people into thinking "feels right" is the initial state of something, I think? You still have to train yourself to get used to a lot of things.