The 23 enigma refers to the belief that most incidents and events are directly connected to the number 23.
Robert Anton Wilson cites William S. Burroughs as the first person to believe in the 23 enigma. Wilson, in an article in Fortean Times, related the following anecdote:
I first heard of the 23 enigma from William S Burroughs, author of Naked Lunch, Nova Express, etc. According to Burroughs, he had known a certain Captain Clark, around 1960 in Tangier, who once bragged that he had been sailing 23 years without an accident. That very day, Clark’s ship had an accident that killed him and everybody else aboard. Furthermore, while Burroughs was thinking about this crude example of the irony of the gods that evening, a bulletin on the radio announced the crash of an airliner in Florida, USA. The pilot was another Captain Clark and the flight was Flight 23.
The 23 enigma can be seen in:
The text titled Principia Discordia claims that "All things happen in fives, or are divisible by or are multiples of five, or are somehow directly or indirectly appropriate to 5"—this is referred to as the Law of Fives. The 23 enigma is regarded as a corollary of the Law of Fives because 2 + 3 = 5.
In these works, 23 is considered lucky, unlucky, sinister, strange, sacred to the goddess Eris, or sacred to the unholy gods of the Cthulhu Mythos.
As with most numerological claims, the 23 enigma can be viewed as an example of apophenia, selection bias, and confirmation bias. In interviews, Wilson acknowledged the self-fulfilling nature of the 23 enigma, implying that the real value of the Law of Fives and the 23 enigma is in their demonstration of the mind's ability to perceive "truth" in nearly anything.
When you start looking for something you tend to find it. This wouldn't be like Simon Newcomb, the great astronomer, who wrote a mathematical proof that heavier than air flight was impossible and published it a day before the Wright brothers took off. I'm talking about people who found a pattern in nature and wrote several scientific articles and got it accepted by a large part of the scientific community before it was generally agreed that there was no such pattern, it was all just selective perception."