FROM LOVE AND RESPONSIBILITY BY KAROL WOJTYLA:
It must be taken into account that it is naturally difficult for the woman to adapt herself to the man in the sexual relationship, that there is a natural unevenness of physical and psychological rhythms, so that there is a need for harmonization, which is impossible without good will, especially on the part of the man, who must carefully observe the reactions of the woman.
If a woman does not obtain natural gratification from the sexual act there is a danger that her experience of it will be qualitatively inferior, will not involve her fully as a person. This sort of experience makes nervous reactions only too likely, and may for instance cause secondary sexual frigidity. Frigidity is sometimes the result of an inhibition on the part of the woman herself, or a lack of involvement which may even at times be her own fault. But it is usually the result of egoism in the man, who failing to recognized the subjective desires of the woman in intercourse, and the objective laws of the sexual process taking place in her, seeks merely his own satisfaction, sometimes quite brutally.
--as quoted in His Holiness: John Paul II and the Hidden History of Our Time, by Carl Bernstein and Marco Politi, Doubleday, 1996.