Earlier quoted context omitted.
For me that doesn't work because then I learn that "yeah you say just walking but we both know it will end up in running." What works instead is I promise I will walk. And then I actually only walk even if I feel like running. That way you will trust yourself. If I say "ok i go to the gym 30 mins. just for a quick training." Then even if I'm in the flow at minute 30, I stop and go home. Next time I remember that and…
Huh? You have a weird "relationship" with yourself. I never did not trust myself anymore if I did more reps than I "promised" myself before. Would a child ever grow distrust against her parents if she changes her mind and wants to do more dishes than initially asked for and they allow her to do it?
So the trick I guess is managing which part of your inner monologue is the child and which is the parent.
I've been experimenting with telling myself "now that I'm at the gym, I'm really enjoying it, I'm really grateful that you dragged me out."