For many people, that weird hole in their budget can be chalked up to one thing: an irresistible impulse to buy something, a need so strong, that nothing else matters.
Call it what you want. Idiosyncratic spending. Heart-and-soul spending. Secret obsession spending. It's about the desires of the heart. And no one is immune from it.
"The way people spend money unmasks them," said Aaron Kipnis, a clinical psychologist and professor of psychology at Pacifica Graduate Institute. "As Warren Buffett said, 'When the tide goes out, you can see who's swimming naked.'"
Kipnis has devoted much of his professional life to figuring out why people spend money the way they do.
"Freud said people are driven by a love of shiny things," he said. "There are certain objects that are imbued with a luminosity, as we call it in psychology. Advertisers try to generate that kind of gleam in their products, objects that represent deep longing."
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Spending that comes from a deep sense of longing should not be confused with the phenomenon of "emotional spending," however. Emotional spending is buying a new pair of shoes after a bad day at work. It's springing for drinks at the bar after getting a raise, or driving home a shiny new sportscar the day the divorce papers are signed.
Conversely, idiosyncratic spending—"soul spending"—reflects a lifetime of longing, fear, hope, love and memory. People spend money for reasons that are deeply personal and continually evolving—reasons as complex as the experiences that inspired them.
Take Brandon Suggs, who has spent many thousands of dollars on thrill-seeking endeavors such as skydiving, bungee jumping, hang gliding, fly boarding and dangerous encounters with wild animals.
An intervention outreach representative at ClearPoint Credit Solutions in Atlanta, Suggs, 30, says he doesn't mind spending 30 percent of his income to do things like "sit on alligators and hold their mouths closed" because—however hard it is to explain to other people—it gives him deep satisfaction.
"When I'm doing these things, it's when I'm happiest and most relaxed," he said. "Paying for it is a hardship, but I don't mind."
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Unlike emotional spenders or compulsive shoppers, idiosyncratic spenders often plan their purchases carefully and understand the consequences of their buying behavior. In fact, they often budget for it or even support it with a second job.
Still, trouble can still arise when their desires overreach their bank accounts.
William "Marty" Martin, a financial psychologist at Aequus Wealth Management in Chicago, recalls a former patient who resorted to embezzling money from her employer to support her addiction to gardening.
"Her thing was flowers," Martin said. "Her garden was choked with flowers. She knew what she was doing was illogical and unethical but she couldn't stop herself."
Psychologists say people who spend their money in unusual or excessive ways are often responding to past traumatic events. The woman with the flower addiction, for example, had been devastated by a series of destructive romantic relationships, Martin said.
Suggs began engaging in thrill-seeking activities the same year several of his closest friends died.
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"When somebody passes on, you realize that life is really not promised to you," Suggs said. "You think, 'I have to live life now.' You'll never experience life like you do when you're about to jump off a building."
Christine Arnone, 45, a dog owner/handler in Salt Point, N.Y., says she is tired of trying to explain her life to people who "don't get it."
Arnone and her husband, Christopher, spend virtually all of their discretionary income on their three prize-winning vizslas, Ginger, Ayva and Annie. Arnone says the cost of dog show entry fees, food, veterinary bills and medication is minor compared to the cost of the RV that transports the dogs to competitions and the 10-acre plot of land they need for exercise.
"People always ask us if the sacrifice is worth it. Would people ask that if they were our children?" said Arnone.
Martin notes that there is an "innate weakness in all of us" that causes people to spend money in idiosyncratic ways—some of which are difficult to justify to outsiders.
"For a lot of individuals, the objects that they buy aren't odd in and of themselves, but it's the amount that's odd. It's the attachment to the object that's extreme," he said.
Nefertari Nelson Williams, an inspirational speaker, says her own childhood deprivation inspired her own quirky spending habits.
"My mom got sick when I was 10, and after that we were homeless," she recalled. "We moved 19 times by the time I was 16. My mentality was, 'just put the money in the bank.' "
But suffering a heart attack in her 30s changed everything, said Willams, 40, of Willingboro, N.J. Clothes shopping for her five children became wild bargain-hunting extravaganzas, with Williams buying out entire inventories of cut-price merchandise and selling it at her own cost to family and friends. Happy to share the abundance, she never tried to turn a profit.
"Shopping is my fun," she admits, giggling. "I don't have a girls' night out. I enjoy seeing my kids look cute and well cared-for. Knowing they're having the opposite life I had.
She adds, "Today my hot water heater broke down. I must admit, I looked at the clothes pouring out my closets and thought, 'Hmm, that could be money in my savings account.' But the joy of shopping outweighs the little bit of guilt that creeps in."
"There are deep currents in the psyche that play out in the acquisition of objects," said Kipnis, who wrote a book on the subject. He calls the process of buying things "complex and emotional."
"I collect 19th century silver dollars—they're extremely beautiful, historical objects ... but collecting them is out of my budget. It's not really harmful, but it's not a very sensible thing. My wife finds it a little odd. So why do I do it?"
He pauses. "When I was a little boy, my stepfather was a gambler and stole my penny collection. Collecting silver dollars has been a very satisfying way to heal that childhood wound."
—By Linda Federico-O'Murchu, special to CNBC.