Seventh-Day Adventists don't like to hear it, but the fact of the matter is that their origins lie in a gross miscalculation and an injury.
First the miscalculation. In the early-to-mid 1800s William Miller, a farmer and amateur Bible student from New York State, began to do some biblical mathematics. Electing to ignore Matthew 24:36, which says that we cannot know the time nor hour of Christ's second return, Miller calculated from the prophecies contained in the books of Daniel, Ezekiel and Revelation that Jesus would return to earth on March 21, 1844. After the date came and went without incident, Miller (and others) went back over his figures and came up with a new date: October 22, 1844.
Miller's followers, known as Millerites, were suddenly given fresh hope. In a sad sidebar, many of these believers saw no need to waste valuable evangelism time with such unnecessary pursuits as planting or harvesting crops. Thus, when the big day came and went without so much as a thunderstorm, they were left ruined, confused and... yes, disappointed.
Now to the injury. Ellen Gould Harmon, a young Methodist girl from Gorham, Maine, was struck in the face by a rock at the age of nine. She almost died from the blow, was disfigured and severely invalided. Her schooling was seriously affected, such that her skills of literacy were of a very basic level.
In 1840 she heard William Miller speak of Christ's imminent return. She was terrified, and found the normal patterns of living extremely difficult to maintain as this news pressed upon her mind. As the date approached she and her parents left the Methodist community and became "Adventists", which literally means "followers of the Advent", or appearance. She was a witness to the frenetic build-up and subsequent anti-climax of October 22, 1844.
Two months later, Ellen Harmon had her first vision. These dream-like "revelations" soon became an almost daily occurrence, and in fact form the basis for many of her teachings and her vast repertoire of books and other writings. These in turn have effectively become doctrinal guidelines for the Seventh-Day Adventist faith. Ellen G. White (her married name) was quick to point out that her insights and teachings were not to be considered as important as the Bible, stating that her words should be seen as no more than an illumination or a guide to biblical teachings. Nevertheless, to speak ill of Ellen G. White from the pulpit of an Adventist church would be seen as tantamount to blasphemy.
In 1994 the Seventh-Day Adventist church "celebrated" - or should that be "remembered" - the 150th anniversary of the Great Disappointment. My brother, who is a shit-stirrer of note, wanted to plan a huge commemorative program for his home church, complete with guest speakers, music, AV presentations, the whole deal. He told me that he planned to cancel the whole thing at the last moment. "Just so they'd know what it felt like," he said.
I asked him if he planned to hand out rocks to hurl at the pastor while he was at it. He thought that sounded like a pretty good idea.