The following statement is a psychological profile review of Adolf Hitler when he was in his twenties. Read it and think about how much it applies to you:
"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."
Well, I lied. This isn't Hitler's profile. Or actually it is, because it applies to fucking everyone's. The above paragraph was assembled from various horoscope statements by professor Bertram R. Forer, who then presented it to five of his students telling each one that is a personalized profile analysis. Unsurprisingly all five believed him and stated that they found the text to describe them personally quite well.
This is called a Barnum Effect named after P. T. Barnum, who's motto was something for everything, and is used by authors when they want to build characters with whom the readers can identify but mainly by horoscope writers. By using general specifics, that is statements which sound really specific but actually apply to a major part of the population, horoscopes trick people into believing that what they read in the daily newspapers actually corresponds to their personality. We all have a loved one with whom we have difficulties this week, we all need a vacation, just as much as we all feel the need to work more and get that promotion and so forth.
Oddly enough, if you take a person who has one sign, let's say Libra, and give them a Cancer (or any other of the ten left) horoscope prediction, with them knowing that it isn't Libra they will most likely shun it. But give them all twelve predictions for this week without letting them know which is which and the chances that they will guess their own fall really low.
Remember: Doubt Everything