Bank regulators on Wednesday sent a message that big banks are still too big and too complex. They rejected special plans, called living wills, that the banks have to submit to show they can go through an orderly bankruptcy.

The thinking behind the regulators’ call for living wills is that if a large bank crash is orderly, there will be no need to save it and no need for taxpayer bailouts.

Pretty straightforward, right? Not for the banks. The regulators deliberately did not communicate the exact things the banks needed to do for their plans to pass muster. In this way, they kept them on their toes — and treating powerful banks this way may end up playing a surprisingly important role in keeping the financial regulation effective over time.

Over the decades leading up to the financial crisis of 2008, banks learned how to sidestep and water down the relatively tough regulations introduced after the crash of 1929. This ability of the banks to get their way was spotted by Hyman Minsky, a maverick economist who died 20 years ago. He was prophetic, too. He identified and warned about the sort of trends in the financial system and the wider economy that helped cause the last financial crisis. That is why when everything started falling apart in 2008, some commentators said a “Minsky moment” had arrived.