Yeah I always wondered what the 99% actually means. 99% of the times you have intercourse? 99% out of 100? 99% per some time frame?

The pill always worried me a bit when younger because most women I knew didnt take it religiously at the same time everyday and it wasnt clear if we were then... 75% safe? 50% safe? 98% safe?

I guess it was enough safe enough for me but I imagine it could have gone the other way pretty easily.

Birth control metrics are almost always phrased as "X % couples having regular intercourse won't get pregnant." So pill and IUD being 99% means 1 / 100 heterosexual couples will get pregnant every year, on average.