[TeMPOraL]

Obviously. But you're saying it like the parents are being selfish here.

Babies need to be fed, protected, cared for and loved. Fulfillment of those needs is, for most people on the planet in the last century or so, directly dependent on the parents' ability to hold a job and earn enough income to pay for housing, food and creature comforts.

Even if sleep training is hard for some kids, their parents losing their jobs or breaking up due to sleep deprivation would be much, much worse for those kids.