There are lots of things we could expect of the viva. A particular length, certain questions, the tone of the discussion, the expertise of the examiners…
And the most fundamental expectation: that the candidate is up to the task. That they have done the work. They have written a good thesis. They are a capable researcher.
If your viva is near, or submission is soon, it’s reasonable to expect you are up to the task.
It’s also common to feel that you’re not. It’s common to be nervous, anxious or worried that you are missing something.
If you feel doubts about your ability then take a deep breath and ask yourself three questions:
What am I really worried about? What can I do to work past that worry? And could I really have got this far if I wasn’t good enough?
You can’t simply be lucky. You’re expected to be good.
And really, you must be good by this stage.