Their judgment was based more upon blind wishing than upon any sound prevision; for it is a habit of mankind to entrust to careless hope what they long for, and to use sovereign reason to thrust aside what they do not fancy.

-- Thucydides, Greek Historian, ca. 5th century BCE (Book IV, 108)

I like Thucydides for the way he tries to explain history in terms of real-politik, people, their drives and especially without including the gods in an explanation, somewhat similar to Hippocrates.

Interestingly, a modern version of this appeared in Neal Stephenson's Anathem:

Never believe a thing simply because you want it to be true

where it's called Diax's Rake.

Anathem is a great book, I'd like to add, and quite well aligned with many of the LW themes.