In America, little girls were glued to the television from before dawn, enthralled by Diana’s dress with its billows of silk taffeta, 10,000 pearls and 25-foot train. To a young girl’s eye, the only blemish of this perfect day was that the bride’s signature feathered hair succumbed to the summer humidity.

But not even flat bangs could detract from the fairy tale dream of marriage played out with such pomp.

Nor was the nobility of the moment lost on adults. As ABC’s Ted Koppel commented that evening:

Today’s marriage between Charles and Diana was … a hugely magnified version of what most of us hope for, the idealized beginning of what is meant to ripen into the perfect partnership of a man and a woman.”

Koppel’s ABC colleague, Bob Green, added: “ The royal aspect almost was secondary. … [T]here was something universal about the ceremony of life that was taking place. The message was the same one that comes through at a wedding in a church recreation room in New Hampshire or a justice of the peace’s office in Ohio.”

When the royal couple said, “I will” (their version of  “I do”), the roar of the crowd outside St. Paul’s Cathedral “was almost as if the world was cheering for itself,” Green reported.

And indeed we do cheer for ourselves when we rejoice in wedding vows.

Marriage is a promise. Not just between one man and one woman, but to the community at large, to generations past and to those yet to be born. Wedding vows set apart this lifelong, life-giving relationship from all others.

That’s why we cheered in 1981, even though, as ABC’s Green also reported, “marriage and the family have fallen on hard times.”

And it’s why the world once again roars with joy as Kate Middleton marries Prince William.

We celebrate their union despite the fact that for Diana, William’s mother, the fairy tale had a bitter, postmodern ending. For the generation of young women who grew up in the age of Diana, her story is a metaphor for the troubled state of marriage today.

The overwhelming majority of young people still desire the marriage ideal, but many are unsure they ever will attain it. The route to marriage isn’t nearly as clear as in generations past, and once entered, its endurance less sure.

Americans are marrying at half the annual rate they did four decades ago, data posted at FamilyFacts.org show. Singleness lasts longer than in prior generations.

The median age of first marriage is five years higher than a generation ago—26 for women, 28 for men. That makes Kate Middleton—at 29, the oldest first-time bride in a British royal wedding—representative of this generation.

As for marital stability: Seven out of 10 couples married in the early 1990s reached their 10th anniversary, compared to nearly nine out of 10 couples married in the late 1950s.

The institution of marriage endures, though, even when a particular marriage falls apart. Our failure to attain it doesn’t change the ideal.

An ideal is not a fairy tale. It doesn’t insist on perfection and doesn’t presume happy endings.

Fairy tale expectations, on the other hand, contribute to inordinate pressures as couples seek to make and maintain a marriage. They encourage brides, for example, to plan the perfect wedding day—to the tune of about $24,000, on average.

“The writers of fairy tales most commonly ended their stories about princes and princesses at the altar,” Ted Koppel intoned 30 years ago. “These writers knew what marriage was meant to be. They were also wise enough to know that it rarely turns out that way.”

Fairy tales, however, leave out the wedding vows, which are meant to dispel the easy illusion of happily ever after, set appropriate expectations for a lifetime of commitment and connect couples to the communities of support around them. The vows begin where the ceremony ends.

Realistic expectations for marriage will go a long way toward making the institution more durable.

That’s why it’s good to hear reports that Will and Kate are going to do their own chores in their royal mansion, rather than hire servants. It’s much more significant news, actually, than Kate’s reported decision to wear her hair down.

Jennifer A. Marshall, director of the DeVos Center for Religion and Civil Society at The Heritage Foundation.