People really do act like contraception is fullproof.
Headline: I can't stop getting pregnant! Mother conceives six times in five years despite using every contraceptive precaution
And look at the comments:
"Yeah right! We should all be so gullible as to believe this!"
"Vasectomy? Sterilisation? Both? The answer is simples people."
"If combined with a condom, there's no way in the world you can get pregnant!"
This belief in the infallibility of birth control is in part what is fueling the abortion rate. The mother featured in the Daily Mail article opposes abortion (thank goodness) but even women who oppose abortion change their minds once pregnant.