I'd say my own journey out of religion provides a good example of this. I reached that "I think I'm an expert" point when I started getting into apologetics for the religion of my birth, Mormonism. I wrote online articles on several topics related to doctrine, mostly focusing on bringing science and religion together. And I engaged in discussions with others interested in tackling the "hard questions", both believers and ex-members. I passed that peak as I started challenging my own cognitive dissonance and realized how little I actually knew, and have been working my way back up the scale in my willingness to discuss these topics as I've finally been gaining actual expertise.

I have seen several examples, but there are a few good historical examples of statesmanship. George W. Bush believing he could 'read' Putin was a well-known mishap. Various examples (perhaps too many to list) of Trump's foreign policy could be early DK effect examples. Later on the curve, George W. Bush was a better statesman at the end of his presidency, after learning all the job he had spent nearly 8 years inhabiting entailed.