“Luck” during a PhD can only come from your working to be in a good space to begin with.
“Luck” with a result or an idea or the final state of your thesis is the result of work, not simple good fortune.
“Luck” in the viva’s outcome denies all you’ve done.
Don’t be so modest. Don’t downplay what you did, and what you can do. Yes, you may have been fortunate, but you still had to work for that opportunity or outcome!