Flashback to one of the earliest posts in this blog: “You’re fortunate, you’re not lucky.”
A tricky question, a tough correction, a difficult discussion – none of these are unlucky. They happen for a reason. You missed something. You made a choice that didn’t come together. You had a lapse of concentration. Some of these things may or may not be beyond your control. But still, you’re not unlucky – that would mean that your PhD and viva were just random events.
You’re not simply lucky if you pass; you’re not simply unlucky if something doesn’t work quite right. And given that a massive majority of viva candidates pass the viva, it’s not likely that you would be unfortunate either.