Kamasutra 2.1.25

2.1.25

upāyavailakṣaṇyād abhimānavailakṣaṇyāc ca//

Vatsya says that this is so, because the ways of working as well as the consciousness of pleasure in men and women are different. The difference in the ways of working, by which men are the actors, and women are the persons acted upon, is owing to the nature of the male and the female, otherwise the actor would be sometimes the person acted upon, and vice versa. And from this difference in the ways of working follows the difference in the consciousness of pleasure, for a man thinks, “this woman is united with me,” and a woman thinks, “I am united with this man.”