Starting a new pack

Anastasia

I used to be on the depo shot and switched to the pill now. I keep reading about people saying if you miss too many pills you have to start a new pack. Why can't you just keep going with the same pack? Are all of the rows a different dosage or something that have to be taken in order? (I tried looking this up on line and it said start a new pack for multiple missed pills but didn't say why.)