To extend on your post, all the failed blocks seem to have one thing in common: too much density. Anything higher than maybe four story high packed or slightly

To extend on your post, all the failed blocks seem to have one thing in common: too much density. Anything higher than maybe four story high packed or slightly higher sparsely packed tends to enter a downward spiral except when "risk groups" are consequently priced out (and even that is only possible in exceptional locations like New York City where low density would be completely unaffordable even for buyers of luxury apartments). In lower density environments (the medium density the article is advocating), the exact same mix of people seems to create much less of that downward spiral. My hypothesis is that it is not the relative fraction of potentially troubled individuals (for lack of better words) that makes or breaks a neighborhood, but their absolute density. No matter how many affluent, stable, nice people you add to the mix, they are pretty much invisible when it comes to creating a positive or negative impression. If "misery per acre" reaches a certain threshold, sad individual fates start influencing each other negatively, multiply and eventually dominate the whole place. Up to a certain, moderate density, stable individuals pull up the troubled, upwards of some undefined density threshold, the troubled start pulling their environment down.