The Forer effect is a specific example of the so-called "acceptance phenomenon", which describes the general tendency of humans "to accept almost any bogus personality feedback".(1)
A related and more general phenomenon is that of subjective validation. Subjective validation occurs when two unrelated or even random events are perceived to be related because a belief, expectation, or hypothesis demands a relationship. For example, while reading a horoscope, people actively seek a correspondence between its contents and their perception of their personality.(1)
The Forer effect is manifested in response to statements that are called "Barnum statements", meaning characterizations made about an interlocutor that the interlocutor finds valid even though the statements are generalizations that could apply to almost anyone. Such statements are used by fortune tellers, astrologers, and other practitioners of chicanery to convince customers that they, the practitioners, are in fact endowed with a paranormal gift.(1)
In 1948, in what has been described as a "classic experiment", psychologist Bertram R. Forer gave a psychology test—his so-called "Diagnostic Interest Blank"—to 39 of his psychology students who were told that they would each receive a brief personality vignette or sketch based on their test results. One week later Forer gave each student a purportedly individualized sketch and asked each of them to rate it on how well it applied. In reality, each student received the same sketch, consisting of the following items:
1. You have a great need for other people to like and admire you.
2. You have a tendency to be critical of yourself.
3. You have a great deal of unused capacity which you have not turned to your advantage.
4. While you have some personality weaknesses, you are generally able to compensate for them.
5. Disciplined and self-controlled outside, you tend to be worrisome and insecure inside.
6. At times you have serious doubts as to whether you have made the right decision or done the right thing.
7. You prefer a certain amount of change and variety and become dissatisfied when hemmed in by restrictions and limitations.
8. You pride yourself as an independent thinker and do not accept others' statements without satisfactory proof.
9. You have found it unwise to be too frank in revealing yourself to others.
10. At times you are extroverted, affable, sociable, while at other times you are introverted, wary, reserved.
11. Some of your aspirations tend to be pretty unrealistic.
12. Security is one of your major goals in life.
On average, the students rated its accuracy as 4.26 on a scale of 0 (very poor) to 5 (excellent). Only after the ratings were turned in was it revealed that each student had received an identical sketch assembled by Forer from a newsstand astrology book.(1)
(1)Wikipedia: Barnum Effect