Almost anyone is capable of cheating, given the right circumstances. The trick is to avoid compromising situations in the first place.

A beautiful young woman comes to visit a middle-aged general while he's living in a war zone, far from his family. They go on long runs where she asks him probing, admiring questions. The general doesn't start out intending to have an affair: He simply sees this woman as a confidante, an ally, possibly someone to mentor. But their relationship does blossom into an affair, with devastating consequences for both the woman and the general, both professionally and personally.

Some have asked how a man as disciplined as General David Petraeus let himself cheat on his wife with his biographer. But when you look at the circumstances—the dangerous location, the distance from his family, the deep emotional bond that developed between the two of them—the question is really, How could he have avoided having an affair?

"A lot of people think, 'You just make up your mind. You're not the kind of person who has an affair,'" said Gretchen Rubin, creator of The Happiness Project. But that's not true—hardly anyone goes into marriage expecting they're going to have an affair, yet more than a quarter of men and 15 percent of women admit to cheating at some point in their marriages.

A few years ago, Rubin posted a thought-provoking list of rules to follow to avoid having an office affair:

1. Never take a first step in flirtation, even in jest.

2. Never have more than one drink with people from work. If that.

3. Never confide details from your personal life to people from work, and don't allow them to confide in you.

4. Never allow yourself to have a "special friend" of the opposite sex (sometimes called a "work spouse") to whom you turn for particular support.

5. Unless it's an unmistakably professional context, don't meet alone with a colleague or client of the opposite sex. E.g, when a client calls with tickets for the U.S. Open, don't go in a twosome.

She's since added two more rules to the list: If you do end up with a platonic "work spouse," make an effort to get to know their family: "that changes things," Rubin says. And if you do find yourself alone with a colleague or client of the opposite sex, ask yourself what your spouse would think if he or she were to walk into the situation. She explains says: "If you imagined your spouse or your partner reading an email or walking into a room, suddenly, would you feel like there's something to be embarrassed about?

What all these rules have in common is that they acknowledge that most people, given the right combination of circumstances, could be strongly tempted to have an affair. The secret is to prevent yourself from getting into a situation where it would be easy to cheat on your spouse.

"People aren't really good at resisting temptation," Rubin said. "It's easier to have a rule that you just follow, so you're not constantly having to weigh circumstances."