I was going to say something similar. Competitions between people does nothing for me (neither motivates nor demotivates), but accountability groups help me a lot to be more consistent or push a bit harder. But I've found that some of my friends really get turned off by the accountability groups, they feel like they're falling behind and end up giving up. Which is disappointing, the accountability groups aren't meant as competitions but encouragement. If you've got someone like me (I can lose weight quickly once I start exercising just a bit more than whatever my baseline is going into it) but your weight is harder to shed, if you see it as a comparison/competition then it can become very discouraging.

Phrasing in things like that matters a lot, how you talk about it and what you talk about.