(LifeWire) -- When Theresa heard her friend was getting married, her heart sank.
Some friends won't take advice or learn from their mistakes.
"I told her I thought it was a mistake," says Theresa. "So she kicked me out of her wedding party. We didn't speak for six months."
And the happy couple?
"Within a year, her husband left her for another man," said Theresa, who asked that her full name not be used.
For Theresa, a medical receptionist in the Adirondacks, this was one more incident that followed a familiar pattern: Her friend picks the wrong man, and Theresa is left to pick up the pieces.
The final straw came when Theresa's friend gave a different boyfriend power of attorney even though Theresa begged her not to.
"I just felt powerless," says Theresa.
Such hard-to-control impulses cause behavior that is not only self-destructive but prompts frustration and anger among friends and family trying to lend a hand.
Roots of self-destructive behavior
"Nobody wants to watch someone they love hurt themselves," says Angela Wurtzel, a psychotherapist in Santa Barbara, California, specializing in "hunger diseases" like eating disorders, self-injury and compulsive shopping.
But in almost all cases, she warns, trying to help will backfire.
What a well-intentioned friend may see as a clear-cut problem with an obvious solution -- an anorexic should eat more, for example, or a compulsive shopper should cut up the credit card -- is something far more complex.
"These compulsions serve a purpose as a self-soothing or coping mechanism for deep psychological pain," Wurtzel says.
This helps to explain the individual's resistance to change -- which frustrates those who try to intervene.
"Friends feel powerless because they are," Wurtzel says. "These compulsions have roots in issues that have taken a lifetime to develop."
"A friend can offer support, but finding the reasons behind the behavior, and breaking down resistance? That's a therapist's job," Wurtzel says.
When the friend you're trying to help can't let go, should you?
"I had to," says Michael, whose attempts to help a friend spiraling out of control after her mother's death were thwarted repeatedly.
"It started with drinking and drugs, then she quit her job, canceled her cell phone, just dropped off the map -- like an animal that goes off to die," says the IT technician living outside of Washington, DC.
Michael, who asked that his full name not be used, said he wanted to help "but in my experience, helping someone who's not ready pushes them away -- and makes you worse, because nothing you do makes a difference."
Michael's friend ultimately sought professional help, but they're no longer close. Theresa has lessened contact with her friend.
"I miss our friendship," says Theresa. "But I don't miss the teary 3 a.m. phone calls."
Helping for the wrong reasons
Despite good intentions, some helpers may be overly invested in fixing friends who can't seem to fix themselves.
"I definitely attract needy people," says Theresa. "When I was able to help (the friend), it felt good -- but that became harder and harder, and she'd blame me for letting her down."
"It's much easier to focus on another's problems than to acknowledge our own," says Wurtzel, who works with patients who repeatedly seek out helper-helpee relationships. "And this can become its own compulsion, recreating a familiar dynamic that's just as self-destructive for the helper."
"If you're compelled to intervene in these situations, ask yourself what you're getting out of it," Wurtzel says.
Finding a balance
According to Wurtzel, the key to helping a self-destructive friend lies in a delicate balance of compassion and boundaries. She offers advice for lending a hand while preserving the friendship -- and your sanity:
• Set expectations, but don't make demands. "An adult relationship is based on expectations, standards and values, with compassion for differences," Wurtzel says. "Demanding the other do things for you and the relationship creates a power struggle."
• Make the other feel heard. "People with self-destructive tendencies expect others to be angry with and abandon them," says Wurtzel. "You can validate their difficulties without condoning the behavior."
• Understand your powerlessness. "If you feel powerless in the situation, it's because you are," Wurtzel says. "The battle of self-destructive behavior is within the person, between them and them."
• Resist the rescue impulse. If someone's always swooping in to save the day, the self-destructive person has no reason take care of themselves. "Lay out your expectations for the relationship, for what you're willing to do and what you expect them to do," Wurtzel says. "It creates the impetus to change."
• Set boundaries -- not for the self-destructive person but for yourself. "Otherwise the relationship becomes unequal, unhelpful and destructive to both people," Wurtzel says. E-mail to a friend
LifeWire provides original and syndicated lifestyle content to Web publishers. E. Bougerol is a writer in New York City.