You're trying to make a point, or tell your child about a decision you've come to. How many times do you find yourself in a give-and-take that goes nowhere?
Kids are experts at deflection. I hear the frustration of parents. I saw it and struggled through it countless times in the classroom. They make a comment or ask a question. You respond and engage, and before you know it, what you wanted to talk about is a distant memory.
Here's a 'for instance': You want to discuss curfew with your tween. You may get some attitude or pushback. Your attention goes to that. Then there is the "What if?" question, and you find yourself drawn into that. In the meantime, the expectation you have for when they come home is no longer the topic of discussion.
How to deal? Quickly acknowledge, then restate your expectations. "I know you are disappointed/wish you could stay out later. However, this is the time we expect you home." "But Mom...." "I hear you, and the decision is still..." Stick to the facts. Stick to the script. Use a cheat sheet if you need one.
When you engage, you lose, and your child knows it will always be just a matter of time before you are worn down. There is no need for arguing or anger. Just give them the facts.