My own startup journey has led me to a contrary belief: At the earliest stages of building a business, being flexible and continuously re-evaluating your assumptions in order to find real market opportunities is more useful than having a lot of passion solving a single problem.
If anything, I've met many many founders who have had too much passion about a single problem, which hurts them gravely when they refuse to consider the possibility that the problem they are passionate about is not a problem at all and they need to pivot.