For the vast majority of Americans — 99 percent, to borrow a phrase — banking is commercial and relatively simple. A checking account, a savings account, a credit card or two. A mortgage, a small-business loan or a line of credit for daily business cash flow.

But at the 1 percent level, where investment banking is done, banking is extraordinarily complicated and extraordinarily rewarding. The risks, as the nation discovered in 2008, are hideous, but that’s what the public is for.

This is why JPMorgan Chase’s admission Thursday that it had suffered a $2.3 billion loss and an $800 million gouge in its earnings from unmonitored derivatives trading is so distressing.

The bank was playing with house money, not client money, and at least some of it was commercial deposits insured by the federal government.

It was as if the 2008 financial meltdown had never occurred. It was as if JPMorgan never had accepted (and paid back) $25 billion in federal bailout money. It was as if the Dodd-Frank financial reform bill never had been written.

It was as if JPMorgan, the nation’s biggest bank, had realized that as a “Systemically Important Financial Institution” it is officially too big to fail and will do whatever it damn well pleases.

To be sure, Thursday’s announcement included expressions of regret for “errors, sloppiness and bad judgment” from Jamie Dimon, the bank’s chairman and CEO. But Mr. Dimon also was defiant

Mr. Dimon insists that the $2.3 billion loss was caused by a traders making “hedging” trades — insuring against potential losses on other trades — rather than proprietary trades involving the larger bank portfolio. The claim is absurd.

Americans have very short memories, but this is the primrose path that led to recession, epic income inequality, deeper deficits and lingering high unemployment. Remember?