Allergies

In the past two weeks, I've learned of three people that I know becoming pregnant by accident. It makes me so angry. Here we are planning our lives around trying to conceive, and these people are just haphazardly getting knocked up! I used to pity these people. I used to shake my head and say to myself, "That's too bad." Now I think something more along the lines of, "Damn it. Hurry up in there!" while looking at my stomach. But honestly, I don't understand how half these people are getting pregnant "by accident". Are they allergic to birth control?