The decline started in the 1950s, when manufacturing generated a hefty 28 percent of the national income, or gross domestic product, and employed one-third of the work force. Today, factory output generates just 12 percent of G.D.P. and employs barely 9 percent of the nation’s workers.

Mass layoffs and plant closings have drawn plenty of headlines and public debate over the years, and they still occasionally do. But the damage to skill and craftsmanship — what’s needed to build a complex airliner or a tractor, or for a worker to move up from assembler to machinist to supervisor — went largely unnoticed.

“In an earlier generation, we lost our connection to the land, and now we are losing our connection to the machinery we depend on,” says Michael Hout, a sociologist at the University of California, Berkeley. “People who work with their hands,” he went on, “are doing things today that we call service jobs, in restaurants and laundries, or in medical technology and the like.”

That’s one explanation for the decline in traditional craftsmanship. Lack of interest is another. The big money is in fields like finance. Starting in the 1980s, skill in finance grew in stature, and, as depicted in the news media and the movies, became a more appealing source of income.

By last year, Wall Street traders, bankers and those who deal in real estate generated 21 percent of the national income, double their share in the 1950s. And Warren E. Buffett, the amiable financier, became a homespun folk hero, without the tools and overalls.

“Young people grow up without developing the skills to fix things around the house,” says Richard T. Curtin, director of the Thomson Reuters/University of Michigan Surveys of Consumers. “They know about computers, of course, but they don’t know how to build them.”