My only point is that, at least in the companies I've worked for so far, a practical Agile implementation must provide some device for making a "pressure" over the team to avoid too many items ending up carried to next sprint.
Of course there are lots of legitimate situations where an item doesn't fit in the sprint and this should be acknowledged, providing inputs for the estimation of the next sprint and making those estimations more accurate. However, in my opinion, it should also be clear to everyone that those slippages have consequences and everybody should be employing their best efforts.
I don't consider this a deficiency in the article though, since Agile in itself seems to be optimistic about teams by its very nature.
I believe this is going to get me some downvotes, but this is unfortunately the reality I live in and if I were going to devise an Agile implementation for my team I would take this into account.