The subprime mortgage crisis of 2007-2008 seems like an obvious example, as is every other bubble. Warnings get ignored because "this time it's different".
To be fair, there often is always someone warning of a bubble. As the famous quote goes, economists have predicted 9 out of the last 5 recessions. The problem is picking out who to listen to. (On the other hand, I don't have detailed knowledge about whether there are more warnings from more reputable sources than usual before actual bubbles).
I'm looking for historical examples of "flinching away," so I can illustrate the concept to others and talk about motivated cognition and leaving a line of retreat and so on.
The ideal example would be one of motivated skepticism with grave consequences. Like, a military commander who shied away from believing certain reports because they implied something huge and scary was about to happen, and then the huge and scary thing happened and caused great damage. Something like that.
What examples can you think of?