I said for months after Teddy was born that it takes five people to take care of a fresh baby (and I should be clear -- that's a healthy, full term baby). I was right. Here's the math (this is the insight -- the math).
Five eight hour days (40 hour) with a half hour lunch break and two fifteen minute breaks constitute a full time job. Yeah, I know we've all worked a lot more (and sometimes, less) hours than this. But this (last I checked) was about the legal definition. Sometimes you get an hour lunch.
Anyway. If you figure the work time at 7 hours, there are 24 full shifts per week in the 24 X 7 world of a fresh baby. They don't sleep consolidated chunks; they often only stay asleep if they are asleep on top of someone who may have to additionally rock the to keep them asleep. They need feedings and changing throughout the day and night. That is, literally, five full time jobs (well, it would be five full time jobs if there was one more shift. Four full time and one near full time jobs).
Once you can share sleep with the kid, it's a little better, but it's still typically more than three full time jobs (16 hours a day works out to 16 full shifts, or three full time jobs and one overtime shift). And if for any reason you can't share sleep with the kid (kid doesn't consolidate sleep at all, adults can't fall asleep that readily, scheduling problems), it stays at the high intensity, five people work level.
Why haven't I seen this analysis anywhere else? Possibly I just haven't read enough books (okay, take ten to finish the hysterical laughter. Twenty if you need it). More likely, this is why. Mainstream parenting (detached/Scientific Motherhood) tries to reduce demands on the parent through a combination of impose-will and gear (playpens, cribs). The attitude is that it only takes that many people to do the work if you are not Smart Enough to Manage the Infant Better. Attachment Parenting people tend to think that if you just go about it more wholeheartedly, it will work out. Oh, and a Really Tight Bond Cures All (sling the baby so you can do chores while the kid eats/sleeps; sleep with the baby to maximize shared sleep; get all of your entertainment/social needs met with the baby, etc.). Neither strategy is willing to accept that it Just Takes More Than Two People To Do All This. And they're all willing to sacrifice everything (get a different job, give up your social life, exercise can wait, etc.) to find the time to care for the child, rather than involve an extended group of people. INSANE!
We used to have extended families (older siblings, etc.) for this. The transition to paid help just wasn't handled well at all.