Expect The Expected
Every viva is unique but no viva should be a great unknown.
Regulations and stories of viva experiences give a shape to the general process; departmental and disciplinary practices give some fine detail to specific viva norms. Taken together these give a general pattern of expectations: you can’t know exactly what will happen, but you can imagine something that the viva will tend towards.
Every viva is different, so you can expect the unexpected – a unique experience – but you can also expect your viva to be like others you’ve heard about in your preparations. You won’t know which details will follow the pattern exactly, or how closely, but unless your situation is very different from every other PhD candidate you can expect your viva to be similar to many past stories.
Every viva is unique but you can expect yours to follow expectations.