Remember the reaction to the writing on the wall at Belshazzar's feast? Old-fashioned Old Testament fear took the fun out of the feast. In Ohio and in Maryland there have been episodes like that, involving savings and loan institutions.

There has been a spurt of panic, some of it reasonably related to the condition of some mismanaged and inadequately insured institutions.

But there is another and remarkably simple explanation for the kind of panic that can produce runs on thrift institutions. The simple explanation is complexity. But, of course, nothing is simple in a world in which a "run" on a bank involves lines of people sitting in line in lawn chairs.

Do you know how your bank works? Sure, you know you rent your money to it. The bank does stuff with it, and makes money, and gives some of it to you in interest and services, such as checks decorated with scenes of Cape Cod. But that is a pretty sketchy knowledge of something as crucial -- if you think about it -- as the whereabouts and activities of your money. But, then, you rarely have to think about it, which is something to think about.

Thrift institutions are examples of this facet of modern life: We are surrounded by things we cannot do without and do not understand. Banks are not incomprehensible. Bankers understand them -- at least some do, somewhat, some of the time. But the rest of us have to take it on faith that the banking system works swimmingly.

We must take much on trust. If we took time to understand everything, we would never get the lawnmower sharpened or the screen door repaired. When that trust begins to crack, it can crumble quickly, producing panic.

A century ago transportation -- say, a horse and buggy -- was comprehensible, in the sense that all the moving parts were visible and uncomplicated. Well, okay, the horse was complicated, but you know what I mean. Today we go to an airport, step into a thin tube of aluminum, are hurled 35,000 feet up and 3,000 miles along, and few of us have even the foggiest notion of how a jet engine works, why a plane flies or how the air traffic control system keeps the planes from bumping one another.

In the 19th century, when doctors were loved, they could not do much for patients, other than make them somewhat comfortable while waiting for nature to heal or kill them. Today doctors are vastly more potent. They also are proportionately less intelligible -- and, not coincidentally, less revered.

In the 19th century, when, of an evening, a family wanted entertainment, it could try conversation (ask grandmother; she can tell you what that was) or books. There was nothing mysteriously technical. Today families stare at devices that bring sights and sounds into their living rooms. Although we are sure there is a reasonable explanation (for the physics of television, not, Lord knows, for the sights and sounds emitted by it), not one American in 10,000 can do justice to a child who asks, "How does that work?"

A flourishing economy, indeed a functioning society, depends on the mass of men and women not thinking about a large and growing number of things they depend on in daily life. One measurement of the modernity of the modern world is the TFGQ -- the Take-for-Granted Quotient. A crucial task -- crucial, although often mundane -- of modern government is to enlarge the TFGQ.

It does this by inspecting restaurants, so customers need not calculate the risk before deciding to trust an unfamiliar kitchen. It certifies the safety of elevators so we never need to make a prudential calculation before inserting ourselves in a box hauled aloft by (I am guessing) pullies and cables and things.

Of course government, as is its wont, often gets carried away and tries to reduce life's risks to zero. Nevertheless, to keep modern society flowing, government must act in many small ways to take large amounts of hesitancy out of life. It does this, for example, when it provides insurance for deposits in thrift institutions. Such insurance removes the drag of anxiety from a crucial social activity -- saving.

"We may fling ourselves into a hammock," wrote Chesterton, "in a fit of divine carelessness. But we are glad that the net-maker did not make the hammock in a fit of divine carelessness." Modern society requires government that looks over the shoulder of, and occasionally nags, the makers of the many networks of institutions on which we depend.