Fortune: Unrealized losses aren’t reflected on banks’ balance sheets due to an accounting practice where assets are held on banks’ books at the value at which they are bought, instead of their current market value. And Stephan Weiler, an economics professor at Colorado State University and co-director of the Regional Economic Development Institute, explained that these losses will only be realized by banks if they are forced to sell their holdings amid a bank run where depositors withdraw their funds en masse.

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