Tried to track down the source for this quote, and found this information from wikiquote.com:
This may well be something Joseph Campbell said in one of his lectures, but it sounds like an approximation to the quote
“Where you stumble, there lies your treasure. The very cave you are afraid to enter turns out to be the source of what you are looking for. The damned thing in the cave, that was so dreaded, has become the center.”
Listed in the first chapter in “Reflections on the Art of Living: A Joseph Campbell Companion” by Diane K. Osbon.