I think a lot of people don't really understand what the purpose of 'Yes, And' due to the fact that it's rarely properly explained.
Okay, so let me take you back to an experience that while not universal is super common especially to use pretend game aficionados:
"I hit you, you're dead!"
"No I'm not!"
"Yes you are!"
"MOOOOOOOM!"
One might recognize this as the reason we use dice to determine meaningful outcomes.
Well, that's also the point of Yes, And.
See, in improv there is by definition, no scripting. You don't know what kind of thing your partner(s) are going to add to the scene, you can only react. If they add something and you shut it down by saying 'no it's not', you're just clogging up the scene and forcing the other person to either reassert their part or come up with something new and abandon what they came up with for something else which isn't just rude and unprofessional for an improv crew, but also means that exchange just wasted the audience's time.
Yes, Anding in D&D is about taking what's given and not wasting everyone's time trying to assert control over the other player by starting and argument or trying to enforce one's authority on them.
None of this says that the action proposed succeeds or has a good outcome, or is an 'I win' button. It's 'let them try' and go from there. It's not getting into a 'not you don't' -- 'I get to choose what my character does' argument.
A player says 'I stab the king'? It's completely valid as a Yes, And to say 'yes, and the guards charge you' or 'yes, and the king convulses, his body contorting until he's revealed to have been a doppleganger', or 'yes, and there is a metallic clang, the king's eyes begin to glow and he says 'you should not have revealed that'. Or hey, sure 'yes, and because this kingdom work on Riddick rules you keep what you kill. Time to figure out your economic policy.'.