The story runs thus:
A psychologist named B. R. Forer apparently gave a bunch of his students a personality test (like a Myers-Briggs test, or one of those stupid Cosmo' surveys), and asked each person taking the test to rate the accuracy of the customized "individual profile" between 0 and 5, ranging from the least to the most accurate.
Unknown to the participants, there was really only one common profile (independent of the choices on the personality test), which read:
You have a great need for other people to like and admire you. You have a tendency to be critical of yourself. You have a great deal of unused capacity which you have not turned to your advantage. While you have some personality weaknesses, you are generally able to compensate for them. Your sexual adjustment has presented problems for you. Disciplined and self-controlled outside, you tend to be worrisome and insecure inside. At times you have serious doubts as to whether you have made the right decision or done the right thing. You prefer a certain amount of change and variety and become dissatisfied when hemmed in by restrictions and limitations. You pride yourself as an independent thinker and do not accept others' statements without satisfactory proof. You have found it unwise to be too frank in revealing yourself to others. At times you are extroverted, affable, sociable, while at other times you are introverted, wary, reserved. Some of your aspirations tend to be pretty unrealistic. Security is one of your major goals in life.
This average score on this and similar studies (repeated a gazillion times) was around 4.2 (pdf original research article, on Scribd).
Our gullibility is shocking, huh?
Here's an YouTube video, for those who don't like to read, or, for those who also like to watch. It's an entertaining video, which shows how little gender, culture, and other elements matter.
If this study was included as a foreword in Linda Goodman's books, I wonder if they would have sold nearly as well.
This has direct implications, not only for "psychic" disciplines, but also on personality test batteries, such as Myers-Briggs.