Personal Incredulity Fallacy
Difficulty understanding how or why something is true does not make it false.
Why isn't "I can't believe it" a reason?
Personal confusion is not evidence. Surprise and unfamiliarity feel like impossibility, but the world is not obligated to be intuitive.
Kirk drew a picture of a fish and a human and with effusive disdain asked Richard if he really thought we were stupid enough to believe that a fish somehow turned into a human through just, like, random things happening over time.
Redressing the fallacy
Invite the interlocutor to reflect on why they find the claim hard to believe, then point them to reliable sources and evidence.