A Common Viva Problem: thinking you have to know and give a definitive answer to every question an examiner asks in the viva.
There may be many cases where this is impossible! While there are lots of questions a candidate can answer swiftly and completely, they do not have to do so for every request. If you’ve not considered Theory X or Idea Y before, how can you give a complete answer immediately? You can’t. So what can you do?
Be reasonable with yourself. Your examiners don’t know everything. They know you don’t know everything. They’re asking questions for many reasons. To generate discussion. To explore. To clarify. Because they’re interested.
If you need time to think, take it. If you need to talk through an opinion, do so. Your examiners do not expect you to know everything. They do expect you to think in the viva.