In the wake of the news that former New York Rep. Anthony Weiner was caught (once again) sexting with a woman who is not his wife, the country let out a collective sigh.

The news was the opposite of shocking, and seemed to affirm the old adage "once a cheater, always a cheater."

But Weiner's case is unusual, because his behavior looks more like a sexual compulsion or addiction, said Pepper Schwartz, a sociologist at the University of Washington and co-author of "The Normal Bar: The Surprising Secrets of Happy Couples," (Harmony, 2013).

"It's about this kind of thrill that he gets showing his body to some anonymous woman, and you call it an addiction or a compulsion when they can't stop it even in the face of catastrophic consequences," Schwartz told Live Science.

But when it comes to more garden-variety infidelity, sneaking around once does not necessarily mean that a person will be unfaithful again, she said.

Sneaking around

Depending on whom you ask and who does the asking, cheating is either the default mode in marriage or the province of a persistent minority: Different surveys have found that between 20 and 72 percent of married people admit to infidelity.

If someone cheats once, there probably is a higher risk that the person will cheat again than there is for someone who has never cheated, Schwartz said, although she noted that cheating is difficult to study because many people won't admit to it. But evidence doesn't back up the notion that past cheating guarantees future misdeeds, Schwartz said. Most people who cheat may have one or two affairs, she said.

"Statistics indicate it's really a small number of people who are serial cheaters, who cheat all their lives, no matter what," Schwartz said.

Often, it's ordinary emotions — such as boredom, ambivalence or unhappiness — that drive infidelity, Schwartz said.

"Often, a lot of cheating happens when a relationship is going sideways or [when a couple is] in hiatus and never made a firm commitment in the first place," Schwartz said.

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Power and sex

But while it's impossible to fully understand Weiner's motivations, the idea of a powerful (or once powerful) man cheating is far from new.

Historically, powerful men have had a so-called license to cheat, and a 2011 study in the journal Psychological Sciencefound that powerful men are more likely to cheat.

"It's really been in the last 150 years that we have begun to hold men to a higher standard of fidelity" than in earlier times, Stephanie Coontz, a historian at The Evergreen State College in Washington and author of "Marriage, A History" (Viking Adult, 2005), previously told Live Science.

What's more, the archetypal politician's personality may make cheating more likely: They are energetic and driven, they have a need to be admired, and they meet lots of people, providing many opportunities for affairs, Schwartz said.

Throw in the throngs of starry-eyed women who are often 40 years younger than these men's wives, and it's not surprising many of them cheat, she said.

"They get way more opportunities than the average guy, which makes them feel like they're not screwing around too much if they're only doing it occasionally," Schwartz said.

Opportunity knocks boots

Even in nonfamous, happy couples, however, the decision about whether to cheat may come down to opportunity and consequences, Schwartz said. For their book, she and her co-authors conducted a survey to see how people would act if given a chance to cheat without any consequences.

"We asked if people would cheat if they knew it wouldn't affect the relationship, and the majority of people say they would," Schwartz said.

Even a sizable chunk of the couples who said they were very happy were open to straying, provided it didn't impact their relationship, she said.

Original article on Live Science.

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