Two ways to get away from failing.
You could just not try.
Failing seems like such an awful thing, best stop now and not go for it. Remove the possibility of failure. Forget all about this doctorate business. It wasn’t meant to be. It wasn’t meant for you. Because if you try and you fail… Well, that would feel terrible, right?
You could look at the viva as one more success you need to get.
Count all of the times you’ve succeeded throughout your PhD. Make a list of all of the achievements you’ve racked up. The number of times you made a difference. All of the things you’ve written in your thesis that have added something to the world. You’ve already done something amazing. The viva is just one more thing you need to do. If you’ve got this far, what could stop you succeeding in the viva?