On your viva day you could be tired. You could forget something. You could be surprised. You could freeze. You could be irritated – or your examiner could be! The train could be late or you could mix up the room. You could lose your train of thought or struggle to find it at all.
Lots of uses of the word “could”.
Could is not a certainty.
It might happen, but it probably won’t.
And even if it does happen, one bad thing doesn’t have to make a bad day.
You can focus on the maybes and mishaps that could befall you or you can focus on the certainty you’ve made. You did the work. You wrote your thesis. You did your preparation.
You got ready for your viva. You can be ready for any bad things that could happen.