You think the worst is over.
You got the kid home from the hospital, you (or your wife) managed to survive labor, you endured the first couple of months of constant wake-ups and middle of the night feedings, and you’ve finally reached the point where the kid is sleeping through the night.
You did it! Success! This baby stuff is a breeze! You start getting a little more sleep, and you finally start feeling like yourself again; you actually, somehow, inexplicably, start thinking about having another baby. After all, you can take two to three months of no sleep. It ain’t no thing!