I've observed the same - unfortunately, first time parents are forced to try out all kinds of parenting experiments on their first-born, before they figure out

I've observed the same - unfortunately, first time parents are forced to try out all kinds of parenting experiments on their first-born, before they figure out how to be "good" parents. And subsequent kids, especially if they have them after some gap, get the benefit of this experience. Add to the woes of the first-born, they not only have to deal with normal sibling jealousy (of having to share their parents affection), but also resolve the emotional issue of why their younger siblings have an "easier" time (i.e. why their parents treat them "differently").