It’s really tempting to have a couple of answers tucked away for the viva, ready for the obvious questions you’ll almost definitely be asked.
But how do you know you’ll definitely be asked those questions? If you’re not, you’ll be asked different questions – questions you’ve not prepared answers for! So then: best to find more questions to have answers for, get them prepped, ready to deploy when the examiner says this or that.
So how many questions to have ready then? 10? 20? 100? More?!
It’s ridiculous when we take it to these extremes, of course.
Preparing answers to every question is a bad idea. Too many plausible questions could come up. You’ll be asked a small number of these in the viva, and probably several more you couldn’t anticipate. Better to focus on answering questions generally than specifically: get comfortable with being asked unexpected questions, rather than happy at being able to recite something for many specific questions.
The exception that proves the rule: make sure you feel happy answering “What’s the contribution of your research to your field?”