Why condoms are packed 3, 6, 12 to a box

A man walks into a drug store with his 8-year old son. They happen to walk by the condom display, and the boy asks, "What are these, Dad?"

To which the man matter-of-factly replies, "Those are called condoms, son.... Men use them to have safe sex."

"Oh, I see," replied the boy pensively. "Yes, I've heard of that in health class at school."

He looks over the display and picks up a package of 3 and asks, "Why are there 3 in this package?"

The dad replies, "Those are for high school boys; One for Friday, one for Saturday, and one for Sunday."

"Cool" says the boy. He notices a 6 pack and asks, "Then who are these for?"

"Those are for college men." the dad answers; "Two for Friday, two for Saturday, and two for Sunday."

"WOW!" exclaimed the boy, "then who uses THESE?" he asks, picking up a 12 pack.

With a sigh, the dad replied "Those are for married men. One for January, one for February, one for March........"