If someone told you the end of the world was tomorrow, what would you do? Sell all of your things? Quit your job? Dawn a white robe and climb and apple tree so you can ascend to heaven faster? These are all things the Millerites did in the 1840s after William Miller told them that Christ was returning to earth.
William Miller was a Baptist preacher and farmer from New York. After devoted studies of the bible, he became convinced that Christ would return to Earth around 1843 or 1844. His preaching and teachings spread quickly, amassing thousands of followers who were known as Millerites. His prediction for Christ's return was October 22, 1844. People traveled across states to be with other believers, and communities braced for the end of the world. When midnight passed and the skies remained unchanged, the event became known as the “Great Disappointment.” Instead of ascending to heaven, believers faced ridicule, confusion, and broken faith.
The aftermath of this event is almost just as interesting. As expected, many of the Millerites completely abandoned the movement as they felt betrayed. Others reinterpreted the prophecy, arguing that Christ had moved to Earth spiritually rather than physically. This reinterpretation eventually gave rise to new religious denominations such as the Seventh-day Adventist Church. What began as one man’s "calculation" ended up reshaping the American religious landscape.
I think this is an interesting event to study as it shows the profound impact of collective belief. Thousands of people trusted Miller so much that they completely abandoned their lives to follow him. They had no evidence besides what he told them! This shows how human nature desires certainty and hope, especially in uncertain times. This is still true to this day. Mass movements, whether religious or political, often rise and fall on the strength of belief and persuasion rather than evidence.
On a micro level, this reminds of the current supplement craze. Somone with a platform can post that some random supplement can help with "mental clarity", "energy", or some other health buzzword. Their "evidence" could be nothing or a "study" that has absolutely zero credibility. This causes people to spend a ton of money on snake oil that doesn't actually help them. While there hasn't been a “Great Disappointment.” within the health industry, it would be interesting to see how many of these brands disappear once/if the FDA regulates supplements.