All zodiac signs are kind of true for everyone, that’s how “it fits” for everyone. They have done studies where they picked random people and gave them random horoscopes (not based on their birthday, just random), and the same percentage of people thought it was accurate as when they gave it to people who really do have those birthdays. In other words, the accuracy of a horoscope has nothing to do with astrology, the stars, when/where/what time you were born, and it has everything to do with the psychology. The human mind tends to make things fit that are close, detect patterns (that may not exist), selectively remember events, ignore things that don’t fit very well, etc.
It’s cool that your critical thinking mind picked up on the fact that it would be weird if people’s personalities were so different based solely on their date of birth. Skepticism is a powerful tool and it can be fun to learn the techniques people use to try to trick you.