Ever since the 2008 financial crisis, policymakers and pundits have wondered what would happen to the cogs of finance in the next big global market shock.

Now, they have a test case to dissect: the widespread market drama that occurred in March as Covid-19 spread worldwide and economies began locking down. While it is still too early to pass definitive judgment on the overall resilience of banks and finance — since the full tally of Covid-19 pain remains unclear — some curious micro-lessons are emerging that deserve more debate.

Consider fixed-income exchange traded funds, which are financial instruments designed to track an underlying corporate bond index. Back in 2008, when worries centred on corporate credit defaults, regulators and investors tended to focus on banks. That was because big investment banks held vast inventories of corporate bonds and acted as market makers in this sector.