Sometimes it’s hard to explain why we need strong financial regulation — especially in an era saturated with pro-business, pro-market propaganda. So we should always be grateful when someone makes the case for regulation more compelling and easier to understand. And this week, that means offering a special shout-out to two men: Jamie Dimon and Mitt Romney.

I’ll come back shortly to the troubles at JPMorgan Chase, the bank Mr. Dimon runs. First, however, let me talk about Mr. Romney, whose remarks about those troubles were so off-point that they constitute a teachable moment.

Here’s what the presumptive Republican presidential nominee said about JPMorgan’s $2 billion loss (which may actually have been $3 billion, or $5 billion, or more, but who’s counting?): “This was a loss to shareholders and owners of JPMorgan and that’s the way America works. Some people experienced a loss in this case because of a bad decision. By the way, there was someone who made a gain.”

What’s wrong with this statement? Well, suppose that someone — say, Jimmy Stewart in the movie “It’s a Wonderful Life” — runs a bank that takes in deposits and invests the money in various ways. And suppose that one of those investments is a risky bet on some complex financial instrument, with Mr. Potter, the evil plutocrat, on the other side.