I’ve heard it said that the Earth is in the Goldilocks zone for planets. Just the right distance from the Sun, just the right composition of elements and so on. If things were a little different: no life, no humans, no Viva Survivors!
The Goldilocks viva would vary I guess. Just the right kind of comments, not too critical. Not so long as to be over-tiring, but not so short as to make the examination meaningless. Impartial but friendly examiners. No unanswerable questions, but nothing that’s trivial.
Your definition might be different. Maybe you really want the circumstances of your viva to be just right, but what can you do about it? Very little.
On the other hand, you can be a Goldilocks candidate. In fact, if you’ve done the work to produce a thesis then you must be just right to meet the challenge of your viva.