If most vivas result in success, why would yours be any different?
If most candidates can get ready with only a little work, relative to the rest of their PhDs, what’s different for you?
If most people have a viva that’s two to three hours long, does it matter if yours is longer or shorter?
If most theses need correcting in some way, what’s the problem with you doing yours?
If you have a real response to any of these sort-of-rhetorical questions, then in most cases you’ll have to do something. You might have to work more, or get more help than most, or ask for support, or get clarification about how your viva can be made fair.
But for some candidates, you might simply have to think about what’s really going on for you. Think about what might be skewing your point of view, and explore what you could do to change your perspective.
Hold on to this: most vivas, the overwhelming majority, result in success.