Thanks for all the feedback. I suspect I am a bit TOO adaptive sometimes. I don't want to violate other people's boundaries, neither do I want to risk being badly judged or inviting hostility, so I mimic a small puddle of water and then regret it a second later. Then I'm angry with myself.
When I was very young I could be too pushy and opinionated. I think I am so keen to never do that again I've gone too far the other way and silence myself. Also, some people would push back VERY hard - or even resort to genuine bullying - so maybe I am afraid to stand up for myself too.