Halle Berry, Sienna Miller, Elizabeth Hurley and Christie Brinkley have a lot in common. Objects of desire by men everywhere, they are beautiful and successful. They've also all had their lovers cheat on them.

Brinkley's hubby Peter Cook is just the latest in a long line of men who wed cover girls but bed other girls.

ED BETZ / STR (ENLARGE)

Christie Brinkley seemed so happy with husband Peter Cook in 2003, long before allegations of his affair with a teen hit tabloids.

DIANE BONDAREFF / Associated Press (ENLARGE)

"Alfie" star Jude Law (above) cheated on fiancée Sienna Miller (below) with his children's nanny.

TAMMIE ARROYO / Associated Press (ENLARGE)

KEVORK DJANSEZIAN / Associated Press (ENLARGE)

Halle Berry was practically glowing next to then-hubby Eric Benét in 2002 at the Golden Globes. But his infidelity resulted in their divorce early last year.

REMY DE LA MAUVINIERE / Associated Press (ENLARGE)

Hugh Grant came clean after he was caught with a prostitute in 1995, apologizing on "Larry King Live" and other shows. But his relationship with Elizabeth Hurley dissolved later.

RELATED LINK: Photos: Famous cheatin' hearts

But why?

Maybe you've wondered why Cook would risk it all for an affair with a teenager he met at a toy store.

Fame, fortune and power offer no protection to cheating, and in some cases, may encourage it, experts say.

"Men do it because they can or an opportunity comes up," said Ruth Houston, New York-based author of "Is He Cheating on You?: 829 Telltale Signs" (Lifestyle Publications, $29.95).

Why men cheat varies wildly. Some hubbies chasing after a new sex partner might be going through a midlife crisis. Some seek an escape from the daily stress and responsibilities of home life and get swept up into a fantasy idea of a sexual adventure.

Most studies suggest almost half of husbands cheat at some point in their marriage. Women are less likely to be unfaithful, according to some surveys. But researchers admit they're really not sure about that — since they've also found women are better at concealing affairs and are less likely to own up to them.

But in the bubble of celebrity, infidelity appears rampant. While engaged to actress Sienna Miller, actor Jude Law hooked up with his kids' nanny.

Actress-model Elizabeth Hurley's relationship to actor Hugh Grant fell apart after he propositioned a California prostitute in 1995. And Oscar-winning actress Halle Berry's second husband, Eric Benét, reportedly cheated on her over and over.

Recent revelations about Albert Einstein's string of young lovers serve as a reminder that cheating is not just a modern-day problem. Letters to and from the greatest physicist of the 20th century showed Einstein going from one mistress to the next, changing them out the way some people grab a new ballpoint pen.

Brinkley announced about three weeks ago that she and Cook had separated. It was Hubby No. 4 for Brinkley. They each had children from previous marriages and have an 8-year-old daughter together.

Cook reportedly said through an attorney he "was stupid, foolish. No excuse."

Still, why do some succumb to the temptation of a quick thrill while others stay loyal? Experts say the spouses who never stray put a high value on their relationships — whether it's for moral, religious or attachment reasons — and are emotionally bonded to their spouses.

"It requires self-reflection. A man might ask himself, 'Do I want my son to think of me as a cheater? How will this affect my wife, my family, myself?' " says longtime family and marriage therapist Karen Gail Lewis, the Cincinnati-based author of "With or Without a Man" (Bull Publishing, $18.95).

Men and women cheat for different reasons. Unlike men, who are driven by sexual desire, women often seek emotional ties, experts say.

"With women, you might have a woman who is 34 years old, and she is juggling so many things, and she looks at her husband, who is snoozing on the couch with the clicker in his hand, and she looks at the mirror and asks, 'Is this all there is?' " said Susan Shapiro Barash, a professor of gender studies at Marymount Manhattan College, who also believes women do a better job at hiding affairs.

Experts say role models also play an important role in whether men and women stray.

Men who cheat, for example, sometimes had fathers who strayed or watched their mothers seemingly accept the digression.

"They will tend to follow that pattern even though they are not realizing it. They are subconsciously programmed to cheat," Houston said.

Debbie Mandel, a stress-management specialist and author of "Turn on Your Inner Light" (Busy Bee Group, $14.95), believes a feeling of dissatisfaction can trigger affairs. Spouses, she said, are more likely to cheat when they feel like a failure at work or home, making them vulnerable to the fantasy idea of hopping in bed with someone else.

"Our culture," Shapiro Barash said, "has an endless fascination with infidelity."

WHY DO THE RICH AND FAMOUS CHEAT?

1. A sense of entitlement: Many celebrities, politicians, corporate executives and other prominent individuals feel that because of who they are, they can cheat on their mates with impunity.

2. Peer pressure: With celebrity infidelity constantly in the news, many rock stars, sports figures, actors and other famous people feel that infidelity is the norm. (Earlier this year, rock star Jon Bon Jovi commented that in the music industry, cheating with women was essentially part of the job.)

3. Low self-esteem: Noncelebrity spouses married to famous husbands or wives sometimes cheat for what experts call "ego embellishment." They want to be the center of attention, to feel important or special. They may actually cheat (consciously or subconsciously) with that in mind.

4. Opportunistic sex: The opportunity presents itself to cheat without getting caught.

5. To satisfy sexual curiosity or the desire for a different type of sex: Author Terry McMillan divorced her husband because of his curiosity about sex with men.

6. The knowledge that they can get away with it: Many cheaters know their husbands/wives won't make waves — as long as they're discreet with their infidelity, keeping it low-key and avoiding publicly embarrassing their mates.

7. Bad role models: Those who watch their dads, uncles or others they look up to cheat will sometimes pattern that behavior.

Source: Ruth Houston, author of "Is He Cheating on You?: 829 Telltale Signs"

5 SIGNS YOUR MAN MIGHT BE CHEATING:

1. Suspicious phone calls

2. Picking fights over trivial things

3. Increased interest in appearance and wardrobe

4. Less desire for sex

5. Unexplained charges on credit card

Important note: Many men, well aware of the obvious clues, will be careful to avoid the typical signs of a cheat. Experts say you should pay attention to subtle signs, such as your spouse gives you a quick look when his or her cellphone rings.

Source: Ruth Houston, author of "Is He Cheating on You?: 829 Telltale Signs"