I used to understand football

Now I'm not too sure.
I'm not sure anyone does.
Simple and honest question: how can a group of 11 talented players, who are all consummate professionals, go from being the best in the world to being incapable of passing a ball three metres to a team mate?
I'm sure, sooner or later, all will be revealed. But for now it is frustrating and, I have to say, rather shocking. 
The most shocking bit for me is that I didn't think the "fine margins" really made all that much of a difference against teams that are not in the same class (and with all due respect to Chelsea, who have a fine recent history, they aren't that good this season).
Sigh.