A lot can happen during a PhD: success and failure, progress and setbacks and halfway stages in-between all of these.
You learn more. You know more. You won’t know everything (probably!) but you’ll gain a perspective that helps you to write your thesis and share your research with others.
Whatever happens along the way, when you reach your viva you can explore your work, describe your journey and show your examiners what you are capable of.
Because now you know what you need to know.
You know enough, can do enough and can show enough.