Agatha Christie once famously said, "The simplest explanation is always the most likely." However, when something shocking or catastrophic happens in our lives, simple explanations just aren't satisfying. We crave deeper reason and meaning and when that isn't given to us, sometimes we create our own. This is how conspiracy theories are often born — someone doesn't like the official account of a major event and challenges it with a different version. Conspiracy theories can attract a wide array of people, from vehement supporters to those who just like a good story. Whether they're somewhat believable or completely ridiculous, the most popular conspiracy theories got that way for a reason — they're just plain fascinating.

1. Lee Harvey Oswald didn't act alone (or possibly at all).

Perhaps only 9/11 comes close to matching the multitude of theories and interest surrounding JFK's assassination in 1963. Kennedy was shot while riding in a presidential motorcade with his wife in Dallas. Lee Harvey Oswald was fingered as the gunman in the Texas School Book Depository that day, but he was shot and killed just two days later, which created a great deal of suspicion. Also, witnesses claim they heard shots coming from a grassy knoll near the motorcade, creating the mystery of the second shooter. The CIA, the Mafia, Fidel Castro, and Lyndon Johnson are often listed as the masterminds behind the murder and cover-up.

2. Princess Diana was killed on purpose.

When the People's Princess was killed in a car crash resulting from overzealous paparazzi in Paris, the public demanded answers. It was hard for them to believe that such a compassionate, celebrated figure could die so senselessly, so it didn't take long for theories to surface about why certain people in power would want her dead. Some think she was pregnant and planning to marry her boyfriend, Dodi Al-Fayed (son to the owner of Harrod's and Paris's Ritz Hotel), and planning to become Muslim, which might've worried the British Royal Family, given her influence on the people. Others state that the family wanted her out of the way so that people would support Prince Charles's remarriage. There are also optimists who believe she faked her death to escape the public eye.