In "The Ascent of Money," Niall Ferguson discusses the complexities of financial products like residential mortgage-backed security collateralized debt obligations (RMBS CDOs). He highlights how the intricate nature of these financial instruments contributed to the difficulties faced in the financial markets. With their complicated structures, there became a growing misunderstanding of these products, leading to increased risk.

Ferguson goes on to explain that as the financial crisis unfolded, agencies started downgrading the ratings of numerous RMBS CDOs. This action reflected the underlying problems in the housing market and the broader economy, revealing the vulnerabilities of such financial products. The downgrades served as a stark indication of the fallout from overly complicated financial systems that were inadequately understood by even the experts.