Why didn’t Achilles wear a boot?
If you know there’s a problem, wouldn’t you try to address it? If you know you have a weak spot, wouldn’t you at least try something?
For example, I knew my background knowledge on one of my thesis chapters was a bit shaky. I just hoped my examiners would focus on the results instead. I could explain how I’d tackled it. I could explain the results. I just crossed my fingers they wouldn’t ask me to explain what a certain kind of manifold looked like and why it was relevant.
Hoping it won’t come up is not a solution: actions help.
If you have a gap in your knowledge, take action. If you have trouble remembering a reference or an idea, take action. If you want to boost your confidence, take action.
Weak spots in your thesis or research probably aren’t as devastating as Achilles’ heel, but if you’re aware of something that could be a problem it’s up to you to do something about it.
Don’t just worry and hope it won’t come up. Do something.