Belief in expert mistakes
A few years ago, there was some publicity around a Navy fighter pilot who claimed to have seen an unidentified object that couldn’t possibly be explained except as an alien phenomenon. Many people considered this to be indisputable proof of aliens. “The pilot is an expert, there’s no way he could have been wrong.”
I am much more willing to believe that someone can make a mistake, regardless of how good they are at the thing in question.
Sure, fighter pilots have excellent vision, and sure, they’re better than I am at identifying objects in the sky. But they’re still fallible. There is no level of fighter-pilot skill that would make me believe aliens visited earth based solely on one person’s testimony.
For any scientific theory, no matter how well-established, you can always find at least one expert with a PhD who studies the topic for a living and disagrees with the consensus. So either almost all experts are wrong, or that one expert is wrong. Either way, experts can make mistakes.