Vaccine hesitancy—the delay or refusal to accept available vaccines despite strong scientific evidence—is considered by the World Health Organization (WHO) to be one of the top ten global health threats, as it frequently triggers preventable disease outbreaks and deaths. This complex, context-specific phenomenon has existed since before the terms "vaccine" and "vaccination" were coined, and is fueled by distrust in public authorities, fear of needles, complacency, and a rampant spread of myths, conspiracy theories, and misinformation. Although vaccines are held to a uniquely high safety standard because they are given to healthy people, serious side effects are extremely rare, yet their very success makes diseases uncommon, leading people to misjudge the dangers of illnesses like influenza and underestimate the value of immunization. While public opposition often centers on civil liberties or suspicions of pharmaceutical profiteering, mainstream medicine shows no serious hesitancy about the overwhelming benefits of vaccination, meaning hesitancy stems largely from psychological biases and a distinct pattern of safety scares. This pattern involves poorly controlled studies proposing unproven adverse effects that fail to be replicated, causing premature alarm and eroding public confidence in vaccines for years.