It would be reasonable to assume that a declining old fogy such as myself—with my 50-something body creaking and wheezing like a car with fading paint, fins, and a clogged carburetor—would be far more vulnerable to swine flu than my bright-eyed teenage daughters. Not so. Two-thirds of the 5,000 confirmed cases in the U.S. thus far, the Centers for Disease Control revealed last week, have struck people between the ages of 5 and 24. Less than 1 percent of those infected were over 65. What gives? Many older people, blood studies show, have partial immunity to the swine variant because of a lifetime of exposure to similar flu viruses. The epidemiological quirk may be counterintuitive, but from my perspective as a parent, not so surprising: Every day I am reminded how vulnerable the young are to hazards to which, due to the inoculation provided by decades of hard experience, I am now immune.

The mean-spirited judgment of others is deeply wounding when you’re 13; at 54, not so much. At 17, the outrageous unfairness of life is not a simple reality, but the source of recurring anger and angst. Into your 30s, everyday blunders keep you up nights, squirming with humiliation and self-doubt. Over time, repeated exposure to these psychic pathogens renders them less toxic; you learn to maintain your equilibrium. What you can’t do, unfortunately, is distill that process into a vaccine to administer to your children. Only through their own mistakes and heartache do they develop antibodies of their own. It is the hardest thing about being a parent, watching your children struggle and suffer, learning what you already know but cannot, for the life of you, pass on.

William Falk