Professor Williams, a mathematics professor at Harvey Mudd College, speaks about the powerful impact of knowing your own body and tracking how it works in this fascinating Ted Talk.
There are a few things I hear over and over again when I talk about NFP. The first is, "Oh! Isn't that what people used before the pill was invented?" The second is, "what do you call people who use NFP? Parents!"
Both bug me for the same reason - they assume that the reason people use NFP is because they have no other options and don't know better. Even more respectful descriptions of NFP often assume that the only practitioners are the extremely religious who refuse all other contraceptives. The fact of the matter is that many smart, educated couples chose NFP to prevent, space, or try for children.