Many a man thinks he perfectly understands women, because he has had amatory relations with several, perhaps with many of them. If he is a good observer, and his experience extends to quality as well as quantity, he may have learnt something of one narrow department of their nature—an important department, no doubt.
 John Stuart Mill, The Subjection of Women (1869). copy citation

Context

“It is only a man here and there who has any tolerable knowledge of the character even of the women of his own family. I do not mean, of their capabilities; these nobody knows, not even themselves, because most of them have never been called out. I mean their actually existing thoughts and feelings. Many a man thinks he perfectly understands women, because he has had amatory relations with several, perhaps with many of them. If he is a good observer, and his experience extends to quality as well as quantity, he may have learnt something of one narrow department of their nature—an important department, no doubt. But of all the rest of it, few persons are generally more ignorant, because there are few from whom it is so carefully hidden. The most favourable case which a man can generally have for studying the character of a woman, is that of his own wife:” source