The following quote is from Acemoglu & Robinson's blog:
This is not to deny that ideology and ignorance play a role in the fates of nations. For example, clearly, if European leaders at Maastricht knew the problems that single currency and implicit bailout guarantees to financial markets on sovereign debt of peripheral countries would create, they would not have opted for it, instead choosing another path to increasing integration in Europe.
I don't think this is right at all. Plenty of economists (both liberal and conservative) were pointing out that Europe was not an optimal currency area and that the single currency wouldn't work.
Instead, I'd say arrogance and over-confidence often play important roles in the fates of nations and the Euro is a prime example.
Other examples? What gets us into trouble more often, ignorance or arrogance?