Most pregnancies during trials of natural family planning occur after intercourse at times recognised by couples as fertile...Indeed, a study of 19,843 poor women in India had a pregnancy rate approaching zero.
If poor illiterate women in India can achieve a failure rate approaching zero, think what educated motivated Americans could do.
By the way, I don't like referring to pregnancy while using NFP as a "failure." I see it as God's Will for that couple at that time in their life.
Agreed.