In February I posted on David Buss being convinced that "true love" exists, even though he’s never seen it and his job is to study love. Similarly, Michael Murrin tells (p.11) how Europeans were immune to being told by Marco Polo how real unicorns (rhinoceroses) differed from what they had imagined:
Marco Polo was careful to disabuse Europeans of various fictional marvels that they then accepted as fact or which had considerable popular support. One case provides a good example. It concerns unicorns. Polo saw rhinoceroses in Indonesia and described them minutely. He ended his discussion with the remark that such unicorns do not resemble at all European notions, nor do they allow themselves to be captured by a virgin. Yet despite the fact that the Divisament dou monde had wide circulation and multiple translations, even while Polo was alive, his attempt to dispel or correct such European fantasies failed. The unicorn survived in tapestries like the great series now shared between New York and Paris and in the spiral horns of the narwhal that resembled the European idea of the unicorn’s horn and can still be found in princely collections.
I’ll bet many who study politicians, celebrities, and scientists similarly believe that ideal versions of these types exist somewhere, even if they have never actually found any examples in their studies. It seems that once we imagine some ideal we have a strong need to believe it exists somewhere, even against all evidence.