If you have even a scintilla of humility about you, if you've ever admitted to yourself that you don't know it all, then you're probably familiar with the impostor phenomenon.

Successful people from all walks of life deal with the impostor phenomenon. It's that back-of-the-head, pit-of-the-stomach feeling that you might be in over your head. That you're pulling one over on somebody. That you're not really deserving of the position you find yourself in.

There is one good part about that doubt: If you feel that way, you might well be deserving of that pay raise, of that attention, of that lofty position among your peers. Because the impostor phenomenon doesn't apply to real impostors, fakes or phonies. They have no feelings of guilt or fear or shame.

The impostor phenomenon most often afflicts high-achieving men and women who simply feel like fakes and phonies.

Apologies if that doesn’t help the knot in your stomach any easier to shake.

The impostor phenomenon can rise up in any of us. In a recent New York Times article, financial planner Carl Richards writes about its effect among those looking to increase their value in the marketplace. "[It's] the moment when you're most vulnerable that all your doubts come crashing in around you," Richards says.

The phenomenon has its roots in a 1978 study by psychologists Suzanne Imes and Pauline Rose Clance, who describe the phenomenon as "an internal experience of intellectual phonies, which appears to be particularly prevalent and intense among a select sample of high achieving women."

Almost 40 years later, the phenomenon is accepted to be alive and kicking in men, too. The original study, though, focused on a group of more than 150 successful women, primarily between the ages of 20-45. They were students, faculty and professional women from areas such as law, anthropology, medicine and education.

Despite their education, despite their positions as high-earners or well-respected members of their profession, many of them considered themselves impostors. From the paper:

"One women stated, 'I was convinced that I would be discovered as a phony when I took my comprehensive doctoral examination. I thought the final test had come. In one way, I was somewhat relieved at this prospect because the pretense would finally be over. I was shocked when my chairman told me that my answers were excellent and that my paper was one of the best he had seen in his entire career.'"

Sound familiar? Clance came up with the Clance Impostor Phenomenon Scale — it's a test that you can take here — to rate how much you feel like you're fooling others, and how much that concern can interfere in your life. She wrote a 1985 book about the phenomenon, too: "The Impostor Phenomenon: Overcoming the Fear That Haunts Your Success." She and Imes are still both in practice today.

Many hugely successful people suffer from the syndrome:

"It's almost like the better I do, the more my feeling of inadequacy actually increases, because I'm just going, 'Any moment, someone's going to find out I'm a total fraud, and that I don't deserve any of what I've achieved.’” actress Emma Watson

"I am always looking over my shoulder wondering if I measure up."Supreme Court Justice Sonia Sotomayor

"When I wake up in the morning, I feel just like any other insecure 24-year-old girl. But I say, '*****, you're Lady Gaga, you better ******* get up and walk the walk today ...'"Lady Gaga

"Oh, God, I struggle with low self-esteem all the time! I think everyone does. I have so much wrong with me. I’m odd looking. Sometimes I think I look like a funny muppet."actress Angelina Jolie

"Part of me suspects I'm a loser and part of me thinks I'm God Almighty."John Lennon

The syndrome, some believe, still may affect more women, possibly due to some inherent differences between the sexes. At least that's what Imes and Clance first suggested: "Unlike men, who tend to own success as attributable to a quality inherent in themselves, women are more likely either to project the cause of success outward to an external cause (luck) or to a temporary internal quality (effort) that they do not equate with inherent ability."

Whoever is affected, there is help. In their original paper, the authors suggest several different types of therapies to address the feelings of inadequacies that come with the syndrome. Once the therapies are undertaken, and the so-called impostor commits to changing the behaviors that undermine a feeling of accomplishment, the patient "begins to be free of the burden of believing she is a phony and can more fully participate in the joys, zest, and power of her accomplishments."

Which is a lot better than feeling like you're getting away with something.