There's a lot that's going down in Greek crisis negotiations this weekend, but if you want to understand what's really happening, then pay close attention to the fairly petty dispute about regulations on Sunday shopping.

Let's get things started with this paragraph from the German memo of things Greece should do (emphasis added):

adopt more ambitious product market reforms with a clear timetable for implementation of all OECD toolkit 1 recommendations, including Sunday trade, sales periods, pharmacy ownership, milk, bakeries, [over the counter pharmaceutical products in a next step], as well as for the opening of macro-critical closed professions (e.g. ferry transportation). On the follow-up of the OECD toolkit-II, manufacturing needs to be included in the prior action;

This is a brief, poorly written reference to a long series of policy recommendations you can read in this audit of Greek economic policy undertaken by the Organization for Economic Cooperation and Development. The Sunday provision is very simple and easy to understand — Germany thinks Greece should change its law so stores can open on Sundays on the same terms as they open on any other day.

What the German government is asking the Greek government to do about this is something that Germany rather infamously declines to do itself. In other words, they think the eurozone would be better off without Greece but they don't want to come out and say so. So they're piling on demands and hoping Greece turns them down.

@mattyglesias Back in '95, I spent my birthday & 1st day in Germany buying food at a gas station, b/c Sunday. I had no idea stores closed. — Amy Burkhardt (@aim4thahardt) July 12, 2015

@mattyglesias Seriously! I remember trying to find TP on a Sunday while living in Munich. — Laurel Justin (@laureljustin) July 12, 2015

It's been a couple of years since I've been to Germany, so I thought maybe the explanation here was that Angela Merkel had some huge change of heart about Sunday shopping and was spearheading a major reform initiative.

But no:

Germany, Europe’s largest economy, is at odds with a trend across the region in recent years to liberalize labor laws that previously kept stores closed on Sundays. As a result, the country’s bricks-and-mortar shops risk missing out on sales as they face stiffer competition from Internet retailers. Two weeks ago, Germany’s top administrative court stopped the state of Hesse -- home to the country’s financial capital of Frankfurt -- from letting libraries, video stores and lottery sellers operate on Sundays, ruling it was protecting the right of workers to have the day off.

And:

Germany is out of step with European neighbors. France announced a plan Dec. 10 to loosen Sunday shopping restrictions as part of Economy Minister Emmanuel Macron’s effort to free up business and bolster growth. His bill proposes extending the number of Sunday openings to 12 a year from five, as well as allow year-round shopping for stores in certain tourist areas.

It's simply not credible to believe that this is a genuine sticking point for the Germans. They are looking for reasons to keep disagreeing.