I think the knowledge of it that exists is incomplete, but I think there's merit to the theory that people's moods are heavily affected by changes in interplanetary gravitational pulls, and based on that it's possible that when you're born, the galactic pull of gravity felt by you as a newborn infant (the most impressionable stage of development for human life) can have significant effects on one's temperament, intellect, and social skills. Although horoscopes are mostly bullshit, most of the Scorpios I know share a lot of very specific traits with me, to say nothing of similar "coincidences" with personality traits and date of birth I've seen among tons of my friends and family.