The question of whom to ask for a dance is not as trivial as it may seem. Force of habit, dancing capabilities, or personal attraction may incline a dancer to dance with the same partner (or a few partners) all the time. This, however, is not helpful to the social dynamics of a dance, therefore dance etiquette speaks out on the choice of partners: To ensure a diversity of partnerships on the floor, and to give everyone a chance to dance, etiquette rules against asking the same partner for more than two consecutive dances.

via dekay.org (http://www.dekay.org/blog/archives/recovering-lost-tango-links)

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