It isn't fair. My only point is that everything a parent does, from the food they feed their children to the books they read them will affect the way that child grows and develops. These small changes have huge effects later in life. This is well documented. And of course humans will always tend to raise their children the way they were raised. And those postitive traits that can be instilled in a child will always reduce economic mobility. So what can be done about it? Can we prevent a person in the upper quintile (your typical HN reader) from feeding their child a balanced diet? Would that be fair? Can we assume that a person in the lowest quintile won't feed their child properly, and take away their ability to do so prematurely a la Minority Report?* That wouldn't be fair either. That's because nothing is fair.

So we are not going to reach 80% mobility out of a quintile. We can't, without producing some sci-fi dystopia. 66% might be ok, I don't really know. But I think the article's presentation of 66% as a problem without much further elaboration is troublesome. Also, I assume (without looking it up) that the author probably selected mobility out of the bottom 20% instead of 10% or 25% or whatever because it probably produced the best "stats" to bolster the claim that mobility is stagnant in the US.

*We can provide them financial support, but we can't make them do anything.