In America, Thanksgiving is always celebrated on the fourth Thursday of November. The next day has become known as Black Friday, which is the unofficial start to the Christmas shopping season. Shoppers have turned this day into the biggest single shopping day of the year. Some stores now open at midnight to get in more sales with all the accompanying shoving, screaming kids and long lines.

But as more and more people turned to online shopping, the following Monday was dubbed the new next best thing, Cyber Monday, with even more hype and discounts.

Now Germans, who don't even celebrate Thanksgiving and are not known for splashing out extravagantly, fear that this retailing development is on the march. Their fears are overstated, because this phenomenon has already arrived. Last year, around 16 percent of Germans shopped online on Black Friday looking for steep discounts.   

The German Trade Association (HDE) says that last year Black Friday and Cyber Monday taken together brought online sales of around €1.7 billion ($2 billion), which works out to be €170 per person on Black Friday and €120 per person on Cyber Monday. This year will surely top that. 

Follow the leaders

But brick-and-mortar stores on both sides of the Atlantic are not giving up and are revving up their offers of discounts, entertainment, extravagant decorations and photo ops with Santa. They need to keep the shoppers they have and in the best case scenario, lure back some of their shoppers who they lost to the digital world.

Read more: China's 'Singles Day' online shopping spree brings in billions

Besides working on their in-store image, many brick-and-mortar companies are also beefing up their own online presence through their websites, smartphone apps or working with other more experienced and well known online retailers like Amazon.

Therefore IHS Markit expects online sales to account for 18.3 percent of holiday sales in the US this year, up from 16.8 percent in 2016. Overall they estimate sales growth of 4.2 percent to about $685 billion for this holiday shopping season.

Not just Christmas markets and mulled wine

Back in Germany many retailing experts think that the German market is saturated. Germans are better savers than spenders. Now in order to entice Europeans to open their wallets, more and more occasions like Black Friday and Valentine's Day are being driven by merchants — most notably by online sellers like the German language sites of eBay and Amazon — obviously using their American bag of tricks.

Yet giving out discounts on a few days a year can be addictive, for retailers and for shoppers. Once buyers start to expect them, merchants must keep giving them. It's a vicious circle.

Saturn, an electronics specialist, is already advertising "Black Week" with the "Best offers of the year." While Amazon Germany is a step ahead with "Cyber Monday Week" which offers new offers every morning at 6am.  

The most common explanation of the name Black Friday is that this is the day on which retailers finally go into the black on the balance sheets. Everything earned after this day is profit. But the more discounts that are offered, the more they will be expected. Selling goods — online or in shops — at full price will become harder.