That’s one way you could look at your PhD and the viva: throughout all of the reading, research and writing you’re storing up exactly what you need for when you sit down with your examiners. Whatever they bring your way, whatever “rain” comes from them, you’ve saved up enough to get through.
On the one hand, there’s some truth to this. Over the course of your PhD you will have saved up enough to be able to pass through the challenge of your viva.
On the other hand…
Whoever said that a rainy day had to be hard, or that a challenge couldn’t be enjoyable?
Why can’t it be true that you spend three or more years building yourself to be who you need to be for the viva – and then arrive to find it a good experience in it’s own right?