The Pill prevents ovulation by acting above the belt rather than below it. In fact, above the neck, in the pituitary. The oral contraceptive has estrogen and progesterone in it. The woman doesn't ovulate. The last seven pills in the pack have no hormone in them, and the lining sloughs like it should, thereby mimicking the normal menstrual cycle but without the release of an egg.
Contraception is achieved.
The pill makes the body think it's already pregnant, temporarily at least, because a steady level of hormones circulate like what happens in pregnancy. This is the ideal case. We must remember that the pill is a fixed dosage, but a woman's body is a dynamic functioning organism. Her body may need a certain amount of estrogen or progesterone to keep the womb's lining intact until her period. And even when we find the perfect one, the pill stays the same but the patient changes, and this perfect pill may no longer be so right for her later.