How many random people do you need to gather together, so that you’ll have a fair probability (50+%) that two people share the same birthday? You need 23 people to cross the 50% mark. Intuitively, most people would guess you’d need many, many more people.
1 – ((1/365)^23) * (365 * 364 * 363 * 362 * … * 343)) = 0,507297
People are intuitively very bad at judging probabilities. This is one of the reasons a lot of people look for metaphysical explanations of coincidences, the chances of which they feel are so small, that they believe it’s not a coincidence at all. This could account for the high number of conspiracy theories out there (which, as anybody who knows me will attest to, I love), or religious or metaphysical experiences that people claim to have witnessed.
I shouldn’t forget this. About myself as well as others.
Another article on probability bias in the Amanda Knox trial: http://www.bbc.co.uk/news/magazine-22310186