Typically Twisted

A practice that is harmful, exploitative, or dangerous—such as pedophilia or public flashing—is deemed abnormal. But outside such clearly damaging obsessions, human-sexuality experts have a general rule: Unusual sexual practices are mostly harmless as long as they are part of a range of sexual responses. If you like dirty talk or get aroused by women's underwear, that's nothing to worry about unless it's the only thing that turns you on.

Then it's usually called a paraphilia, defined as unconventional sexual behavior that's both obsessive and compulsive. For instance: A guy who can get off only when he's wearing diapers, or a woman who insists on dominating her partner. The person "is now substituting a behavior for a partner, and the behavior has become necessary for sexual satisfaction," sex educator and author Yvonne Fulbright explains.

A little bit of kink is a good thing if it spurs open-mindedness and a spirit of adventure. But when an object or a ritual becomes more important than the living, breathing partner, it gets in the way of a relationship and of sexual fulfillment.

The predilection doesn't have to be weird to cause a problem. Fulbright says that increasingly, she hears from heterosexual guys who have trouble getting aroused unless they look at or imitate porn. At first, their counseling regimen is not very much fun: "It's almost like quitting smoking," she says. They have to slowly get used to new (non-porn-related) practices over time, while tolerating unpleasant feelings akin to psychological withdrawal.

But over time it becomes easier for them to respond to a wider repertoire of sexual situations. "It's a matter of allowing variety in and keeping a sense of exploration," she says. "Otherwise sex becomes very selfish."

An Infinite Loop

I've got a torturous secret.

A lot of innocent-looking people are hiding impressive peccadilloes: drug addictions, health problems, financial troubles, infidelity. We even keep secrets from those closest to us: More than 70 percent of married men and women keep stashes of money that a partner doesn't know about, one poll found. Secrets like these may be ordinary, but they often take on a terrifying influence that grows stronger as you put more effort into hiding them.

The simple act of concealing the truth bestows a lot of emotional power on a secret. Even small, trivial falsehoods or omissions begin to loom large as you struggle to keep them under wraps. You become obsessed, and your shame fuels your obsession.

The holder of a shameful secret fights irresistible urges to confess, as Frank Warren of postsecret.com might attest. As part of an art project, Warren began encouraging strangers to write their darkest thoughts on hand-made postcards and mail them in anonymously. Since 2004, more than 200,000 people have responded. Each week, a new set of postcards goes up on the site, with confessions ranging from the poignant to the hilarious. "I don't love you anymore." "I didn't tell my wife our son was injured in Iraq." "I'm 27 years old, and I'm a virgin."

The effort of keeping a secret actually prompts you to think about it more, psychologist Daniel Wegner of Harvard University has found. Part of your brain is constantly monitoring it, trying to make sure you don't blurt it out. This screening process unintentionally keeps the subject alive in your memory. Intrusive thoughts about it pop up, distracting and alarming you, and making whatever you are hiding seem much bigger and more twisted than it is. In his research, simply forbidding a subject from thinking about a white bear can make it extremely difficult to stop thinking about the pesky thing. "If there's a general rule, it's that when you keep a secret, it's going to be something you'll think about a lot," he says.

"That's why hidden love affairs become so potent," Wegner adds. "The attraction is magnified by the effort of keeping it secret." Confessing can weaken the sway, he notes. And for those sins that are just too big to admit to face-to-face, there's always postsecret.com. You might find that someone else is carrying the same burden as you—and suddenly, it will seem a little less horrifying and a little more human.

Solitude is Bliss

I like to be alone.

Thanks to guys like Ted Kaczynski and Seung-Hui Cho, modern loners have a bad reputation as misfits and misanthropes. It is true that some of the worst murder sprees have been committed by social outcasts. But a solitary gunman usually winds up that way because he is so deranged—or so difficult—that he cannot find a niche in normal social life. His vengeance is fueled by rejection. He wants to fit in, but he can't.