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In the 1970s, Thomas C. Schelling proposed a model which claimed to show that a high degree of spatial segregation can result from individual preferences which do not in themselves aim to achieve such a degree of collective segregation. However, the present paper demonstrates that this model contains several structural constraints which totally explain the obtained levels of segregation. A real weak individual demand for similar neighbours leads to low social segregation and a strong demand leads to high segregation. The levels of entropy that are globally achieved for a given threshold of individual satisfaction are not at all surprising in relation to the laws of chance and to what each individual actually wishes. The Schelling model does not allow to conclude that, in general, large ghettos are resulting from innocent decisions.