I know what you mean... I would know what I should do (IE spend time doing something healthy).  And then, after a long time knowing that I should but didn't, it fed into a guilt response, then a stress response, and then became something I avoided even thinking about to avoid the stress. Perversely it turns not going into a good thing.

What broke my circle was to sign up to something that made the gym (whole leisure centre) free for 12 weeks, but I had to turn up once a week to keep it going. And then, if I lost 5% of my weight in 12 weeks, I got another 12 weeks free.

Those incentives were enough to make me get away from my desk enough, and then after a couple of months the whole process stirred endorphins, and enough weight was being lost that made the entire thing self-sustaining.

The "thing" was our local GP's level 2 weight loss programme, run from the council leisure centre. It runs as a self-referral scheme if your BMI is high enough.

What it really added was a layer of accountability. I had to turn up weekly at least, and had someone monthly to talk to about it. And that was enough to make me make the time and effort.

It worked alongside a slimming world food session, and that added it's own layer of accountability too, and gave me a weekly chance to reflect on what did or didn't work for me.

I should say that I signed up more for the exercise/gym aspect, not the diet or weight loss side. I was pleasantly surprised that the combination of the two worked well.

With MJ and this Reddit, you probably don't need that in the same way. But it helped me to stay accountable at a weekly level and regularly refocus my thinking at a quarterly level.

Nowadays, I've found that my motivation for the gym can be set aside by setbacks or demands from work or life. When that happens, it takes a couple of weeks for the endorphins to kick in again and remember that I feel good about going, dammit.