In the viva you may have to defend your work. Ideally, you need to do so without becoming defensive.
Defending: “This is why I made this choice…”
Defensive: “I made the right choice!”
Defending: “…that’s a fair question. I think…”
Defensive: “…that’s not relevant because…”
Defending: “…well, I think I addressed this point in Chapter 3…”
Defensive: “…oh yeah? Well what would you know!”
Stay on the right side of defending in the viva. No thesis or PhD is perfect. You can defend, explain and explore your decisions and conclusions, of course, but don’t make it personal. Make your examiners’ comments about the work.
Take a step back and breathe if you feel that you’re being criticised. If your examiners don’t agree, ask them why. Listen and then bring it back to what you did and why. That’s what will help your answers.