possibility of pregnancy?

Okay so this hasn't happened to me yet but just to be safe than sorry, if, for instance, the condom broke while being on the birth control pill let's say...for 2 months, would you still get pregnant? It just confuses me because if your on birth control pill, shouldn't it highly stop you from being pregnant because it's "birth control"? Like I heard of people getting pregnant on birth control and I just thought it was crazy.