We middle-class Americans are in a funk. “The overarching economic narrative of the 2008 campaign is the idea that life for the middle class has grown more difficult,” Paul Taylor of the Pew Research Center, which recently published a massive report on middle-class anxieties, writes. By its survey, more than half of Americans believe they either have not moved ahead in the past five years (25%) or have fallen behind (31%). Pew pronounces this “the most downbeat short-term assessment of personal progress in nearly half a century.”

It’s not that Americans have lost their optimism. About two-thirds say they have higher living standards than their parents did at the same age, and by a 2-1 margin they expect their children to live better than they do. But there’s an underlying disenchantment that seems to predate today’s higher oil prices, falling home values and declining employment.

“When my college-educated, gainfully employed thirty-something friends and I get together, we talk about money,” Nan Mooney writes in her new book, “(Not) Keeping Up With Our Parents.” “We talk about our inadequate health insurance and whether we can afford it, about how to juggle credit card payments and crushing student loans. … This wasn’t the life I’d expected.”

Part of the deceptive sense of falling behind reflects the elastic nature of being middle class. According to Pew, 70% of households now have two or more cars, and a similar share has satellite or cable TV; 66% have high-speed Internet; 42% already have flat-panel TVs. Thirty years ago, no one’s parents had this inventory. More students go to college and graduate school, so more have debt. Health care is expensive in part because modern medicine can do so much. Someone has to pay. One in 10 households now has a vacation home.

“Progress” keeps draining our pocketbooks. Pew finds that four-fifths of Americans find it hard to maintain middle-class lifestyles; in 1986, two-thirds did. But today’s middle-class anxieties transcend the well-advertised “squeeze” on incomes. The deeper source of disquiet, I think, lies elsewhere. Middle-class families value predictability, order, and security, and these reassuring qualities have eroded. People worry about rising living expenses; but what really upsets them is the possibility that their incomes or fringe benefits — pensions, health, and disability insurance — might vanish.

Paradoxically, “the lives of individual Americans have grown simultaneously more prosperous and more precarious,” Peter Gosselin writes in his new book, “High Wire.” Mr. Gosselin, a Los Angeles Times reporter, has provided the most thorough account of this phenomenon to date. As he shows, the chances of being hit by a life-altering event (a long spell of unemployment, divorce, a big decline in work hours for one spouse) have declined slightly since the inflation-plagued 1970s and early 1980s.

But the consequences of setbacks have grown, he finds. The share of families suffering a 50% loss of income with a spell of unemployment rose to almost 26% from 17%. Fear of these setbacks has also climbed up the social ladder: not just factory workers and low-paid service employees but also managers and engineers.

Companies downsize. Older workers exit in buyouts. Companies raise health-insurance premiums. The reliable “defined benefit” pension (which paid a fixed monthly amount) has given way to the riskier 401(k) — vulnerable to bad investment decisions and sinking stocks. Corporate protections have weakened, as Mr. Gosselin notes.

One result is that bad economic news packs greater psychological punch than it once did, because more people identify with the victims. Change isn’t just something that happens to them; it could happen to us. People worry even if they hold well-paying jobs.

We are losing our sense of entitlement. Under the implied social contract, people who “played by the rules” — to use a phrase popularized by Bill Clinton — deserved modest middle-class guarantees: a steady job, rising income, and protection against random misfortune such as sickness, disability, job loss, and accidents. There was a belief that diligence and responsibility were their own rewards.

It’s worth noting that this imagined entitlement never universally existed. Between 1975 and 1984, unemployment averaged 7.7%; today’s is 5%. The now venerated defined-benefit pensions sometimes weren’t fully funded, so that promised benefits weren’t always paid, or were funded at the expense of the next generation. Today’s retired and well-pensioned autoworkers have condemned those who followed to lower-paid jobs or no jobs at all.

Almost all Americans consider themselves middle class. In the Pew survey, 53% put themselves in the “middle class” and 19% each in the “upper middle” and “lower middle” classes. But the prevalence of middle-class ambitions and values creates a vexing contradiction: The advances in living standards that Americans expect require a flexible and competitive economy that weakens the security and stability that Americans also expect.