Tadpole had a terrible time falling asleep in her crib. Sprout really likes falling asleep in her crib.
Tadpole was great at falling asleep in car seats and strollers. Sprout not so much.
Tadpole had trouble self soothing, Sprout figured out sucking her thumb very quickly.
Tadpole woke from naps if I moved around even a little bit. Sprout's got the hang of getting herself back to sleep.
Sprout takes one good morning nap, then short naps later in the day. Tadpole (once she fell asleep) could sleep a long time whenever she was tired.
I point this out because as every parent knows, lots of people like giving parenting advice. There are books out there with parenting advice. Some of the books are good. Some of the advice from people is good.
Even if all advice was good and based in experience and research and things, it would run into the basic problem that kids are different. Granted we have more experience than we did with Tadpole, but I don't think that we're the cause of all of the sleep differences above. Kids are different. Even good advice doesn't always apply.
That's worth keeping in mind.