I think it also helps to give people multiple reasons for making a change. So for example as a household we changed our diet by only have meat once a week now, combination of health and environmental benefits pushed us to make the change (Could never go fully vegetarian though).
Pushing people to walk/cycle works because you have both environmental/health arguments.
The difficult one is encouraging people to not excessively heat their houses (we should all be turning our thermostats down a couple of degrees), but maybe cost is a factor there.
Besides, we don't have to scupper our quality of life. Nuclear remains on the table, for example. And it turns out thumb-twiddling for long enough has made wind & solar competitive and they're getting better. The biggest win would be cutting down population sizes and that seems to be happening naturally because it enables people to live more comfortable lives.
The cloud of massive inequality and diminished opportunities for people of childbearing age has a silver lining after all...
I don't think that's the case. It's a coordination problem. People don't want to reduce their quality of life if they don't know for sure that others won't do that as well. Most things in life and in human psychology are relative, in constant comparison to our peers.