I am getting increasingly frustrated with this on a site which is supposed to support mums and women. Someone will post for advice relating to an accidental pregnancy, and you can pretty much guarantee within the first 2 pages some prick will come along and ask "well how did it happen?". Errr quite frankly its none of your business and doesn't really relate to what the OP is asking.
It is judgemental, unhelpful and none of you bloody business. There are plenty of reasons birth control fails. Actually when you look at developments in BC effectiveness hasn't really changed for decades- availability and impact on pleasure has, but not effectiveness.
The reckon 50% of births globally are accidental pregnancies, and in the UK and UK that number is still 40-50%
When your doctor tells you about effectiveness rates, that is for one off encounters, the way the % compound over time means the failure rate is actually quite staggering, as illustrated here. https://www.nytimes.com/interactive/2014/09/14/sunday-review/unplanned-pregnancies.html
I dont think this perpetuation of these myths that unplanned pregnancies must be "someones fault", and us as women allowing these judgemental comments to go unchecked on this site is in anyway helpful.