Ohhhh, so that's why!

A young boy and his father were in a store when they walked past a rack of condoms. Being a curious young lad, the boy asked his father, "What are these things daddy?" His dad said, "Condoms son." The boy asked, "Why do they come in packs of 1,3, and 12?" The dad replied, "The packs with one are for the high school boys, one for Saturday night, the ones with three are for the college boys, one for Friday, Saturday and Sunday, and the ones with twelve in them are for the married men, one for January, one for February, one for March...."