You will almost certainly lose some things over the course of a PhD.
Probably you’ll lose track of good ideas. You’ll forget the name of an author. That little project you were going to do. That section you were going to write. Perhaps even a chapter that just won’t fit with everything else.
Whatever you lose or forget, don’t forget you will find far more than you lose.
Ideas that make a difference. Skill, talent, ability. A thesis that matters. Confidence in your self, I hope.
Think about what you’ve lost in preparation for the viva, but only a little; don’t forget that your examiners really want to hear about what you’ve found along the way.