coincidence

alt=An image of a total solar eclipse at Orin Junction, Wyoming in 2017. A total solar eclipse happens when the Moon completely blocks the face of the Sun. It is the result of a cosmic coincidence. Even though the Sun is about 400 times bigger than the Moon, it is also about 400 times farther away. This makes the Sun and the Moon appear almost exactly the same size in our sky. |thumb|Solar eclipse of August 21, 2017|A total solar eclipse at Orin Junction, Wyoming in 2017. A total solar eclipse happens when the [[Moon completely blocks the face of the Sun. It is the result of a cosmic coincidence: Even though the Sun is about 400 times bigger than the Moon, it is also about 400 times farther away. This makes the Sun and the Moon appear almost exactly the same size in Earth's sky.]] A coincidence is a remarkable concurrence of events or circumstances that have no apparent causal connection with one another. The perception of remarkable coincidences may lead to supernatural, occult, or paranormal claims, or it may lead to belief in fatalism, which is a doctrine that events will happen in the exact manner of a predetermined plan. In general, the perception of coincidence, for lack of more sophisticated explanations, can serve as a link to folk psychology and philosophy.

From a statistical perspective, coincidences are inevitable and often less remarkable than they may appear intuitively. Usually, coincidences are chance events with underestimated probability. An example is the birthday problem, which shows that the probability of two persons having the same birthday already exceeds 50% in a group of only 23 persons. Generalizations of the birthday problem are a key tool used for mathematically modelling coincidences.