Jack, an entrepreneur, had just turned 40, and life was good. He and his wife, Amy (their names have been changed), had three kids and were well-liked in their small suburban town in New England. Then Jack started a home-renovation business, threw himself into his work, and hired a 26-year-old guy who was new to town to be his assistant. Not long after, Amy offered to show the kid around. She told Jack that she was helping his assistant find an apartment, but actually the two of them were sneaking off to a hotel to have sex—regularly. When Jack found out, Amy revealed the hard truth: This guy may not have been husband material, but he was far more interesting and exciting than the absentee spouse Jack had become. He was charming, handsome, and apparently unfazed by the fact that Amy was married.

If you think your wife is going about her daily routine—exercising, working, shopping, taking the kids to after-school activities—without encountering guys who want to sleep with her, you're delusional. She's being hit on all the time. The constant barrage works like conception: Only one of those wriggly bastards has to get through to change your life forever. And the guys crossing her path are a different breed from the ones who were on the prowl even a decade ago. Take the yoga instructor. He's the modern equivalent of Warren Beatty in Shampoo, and his core strength—and genuine way with your wife's Kundalini—isn't lost on her. Then there's that brooding, troubled ex she gets a drink with every now and then. This guy makes her feel needed—in a way that's very different from the way you do when you get home from work and tell her all about your lousy day. The other men she interacts with daily—the stay-at-home dad down the block whose daughter is friends with yours, the boss who so generously gives her flexible hours, the twentysomething soccer coach who looks at her like she's a 21st-century Anne Bancroft—have a hold on her affection simply because they're around when you're not. And what all of these men have in common is that they present a refreshing alternative to, well, you.

"Women having affairs aren't looking to replicate the feelings in their marriage," says Susan Shapiro Barash, the author of A Passion for More: Wives Reveal the Affairs That Make or Break Their Marriages. "They're looking for what they can't get in a marriage. If you're married to a brain surgeon you don't go for another surgeon—you go for brawn. If you're married to a plumber, you might be drawn to a professor when you go back to school at night." And if she's shackled to a workaholic, she might be drawn to someone who isn't consumed by ambition.

"I see more women who cheat than men," says Tina Tessina, a psychotherapist and the author of The Commuter Marriage: Keep Your Relationship Close While You're Far Apart. Barash estimates that close to 60 percent of married women have had extramarital sex.

"With men's affairs, it tends to be not enough sex—with women it tends to be not enough attention and interaction," Tessina says. According to Barash, most women feel an "unrelenting need for romance and excitement." And they're not getting them in the half-hour they spend flipping through magazines while you watch The Daily Show every night after the kids go to bed.

Now think about a yoga session, a one-on-one parents' coffee hour after the playground, a post-soccer-practice chat in the parking lot, a brainstorming meeting over a lunchtime bottle of Sancerre. Connect the dots, familiarize yourself with the new other-man archetypes, and consider looking up from your P&L report once in a while.