The Whole and The Parts
To get ready for your viva you need to focus on the whole of your research, your thesis and your PhD journey. You need to know that your examiners could ask you about everything: why you did the work, how you did it and what happened. What you learned, what you know, what you can do.
To get ready for your viva you need to focus on the parts of your research, your thesis and your PhD journey too. You need to narrow your focus to what really matters. What are the key papers that helped? What outputs or outcomes matter? What successes have helped you the most?
You have to consider the whole. You have to consider the parts.