ok how effective is birth control??

Mary
I am on it and have been for years but i still dont rely on it because i have heard girls getting pregnant on it so i always use condoms as well just in case... is it safe to let a guy nut in you in bc or no? 
And how issit possible to get pregnant when you take it right same time each day & never miss a pill?? Are these girls just super fertile or their partners have superman sperm or what??