indeed, this is pretty basic re: negotiations
people who don't get that perhaps are among the people who don't quite grasp that it isn't a good idea to say unilaterally guarantee rights for EU nationals in the UK without reciprocal rights in place for UK nationals in the EU
The basic problem seems to be that some people have literally no clue how to negotiate. You have to have red lines, you have to be willing to walk away and you cannot let the other party dictate the rules otherwise you will get screwed over.
It's almost like some people want the negotiations to go badly...