Why are duplicate tuples not allowed in a relation?

Tuple refers to a row in a table that represents a set or collection of related data values. It corresponds to the relationship which represents entity type as a set of tuples, where each tuple is an ordered list of values corresponding to attributes of relation. As each tuple represents a distinct data record entity, so no two tuples in a relation (i.e. a table) can have the same combination of values for all their data items. Moreover, if a new tuple is added in the relation, then it should not reflect the existing data-values, otherwise, it will violate the uniqueness constraint and the relation as a whole will not have a minimal super-key.