Stories can be very persuasive.
Do you have a story that says you need to do this or that in order to be ready for the viva? You might be unable to not listen. You might have to wear those socks or listen to a certain song in order to feel right to talk with your examiners.
Or do you have a story that says you can’t do certain things? You might need to avoid drinking coffee because you feel it makes you twitchy. You might need to avoid a colour because of an association you have with it.
Perhaps you even want to avoid walking under ladders, seeing black cats or scheduling your viva on Friday the 13th!
Superstitions are stories. They can feel true, but they are only stories we tell ourselves. Rather than do this or avoid that before the viva, perhaps it’s better for you to try to create some new true stories.
What’s the story of your PhD, for example?
How did you get from the start to where you are today?
What are the things you could do to boost your confidence?
What stories are you telling yourself before your viva?