A natal chart is computed from date, exact time, and location; the ascendant degree, the chart's anchor, cycles through the zodiac roughly every two hours, so birth time is the sensitive variable. Courts historically employed astrologers, and birth data of elites was politically valuable: astrologers were prosecuted for casting royal horoscopes, notably under English statutes against calculating nativities of the monarch, such as the 1581 act (23 Eliz. c. 2) targeting prophecy about the queen's lifespan.
Modern psychological astrology reads the chart as a map of tendencies and timing windows rather than fixed fate, a framing popularized by twentieth-century figures like Dane Rudhyar (The Astrology of Personality, 1936). The roadmap metaphor survives every debunking because it asks for interpretation, not verification.
The older doctrine, from Hellenistic texts like Vettius Valens' Anthology (2nd century CE), is harder: the moment of birth imprints a fate-structure, and knowing someone's exact data was once considered a route to power over them. The modern privacy instinct around birth times is a fossil of that doctrine.
If a birth chart is a probability map drawn from when and where you arrived, what was the sky doing at your coordinates?