The first viva must have been really awkward.
What questions would the examiners ask? How might the candidate know what to expect? How would the examiners know what to expect?!
Who decided what made a good thesis? Or if the candidate had done enough? Or if they did enough in the viva?!
Why were they even having a viva???
Of course, the viva as we know it today is an evolution of former practices. Structure given to culture, rules to rhythms. That’s not a bad thing: it may be tricky to pinpoint exactly when and where PhD vivas started, but we know where they are now.
For your viva you can know what to expect. There are regulations, expectations and experiences to frame your understanding. Your viva might feel a little awkward and uncomfortable, but I’m sure it will be much better than the experience of the candidate at the first viva!