Jamie Dimon, the chief executive of JPMorgan Chase, can be clear as a bell when he denounces financial reform. But on an emergency conference call with analysts on Thursday to announce the bank’s stunning $2 billion trading loss, his message was frustratingly vague.

The loss, according to Mr. Dimon, was in the bank’s “synthetic credit portfolio,” which presumably means it involved the same type of complex derivatives that played such a destructive role in the financial crisis. And Mr. Dimon said that sloppiness, bad judgment and stupidity — his own and his colleagues’ — had led to the loss.

It was a stunning admission from a man who led JPMorgan through the crisis relatively unscathed, but it doesn’t explain what actually went wrong.

What Mr. Dimon did not say is that the loss also occurred because of a continued lack, nearly four years after the crisis, of rules and regulators up to the task of protecting taxpayers and the economy from the excesses of too big to fail banks; and, yes, of protecting the banks from their executives’ and traders’ destructive risk-taking.