This quote is about biological viruses, but it has metaphorical power in thinking about regulating new and exotic financial instruments:
Investigators face a daunting black box with emerging viruses: the challenge of developing a universal therapeutic agent to combat a genetically proficient virus that quite likely has many more options for emergence than we have yet considered.
–Graham, R., & Baric, R. (2009). Recombination, Reservoirs, and the Modular Spike: Mechanisms of Coronavirus Cross-Species Transmission. Journal of Virology, 84 (7), 3134-3146 DOI: 10.1128/JVI.01394-09