Robin
In Belgium, everyone over the age of 15 must always carry their ID card. This law dates back to the Second World War, from 1940 to 1945. The Germans forced Belgians to carry an ID card. This has never been repealed in Belgium.
Interesting. Even in Germany this is not mandatory what the Nazis once forced upon us. Sure, you need to have some sort of personal document, but you can chose whether you prefer a “Reisepaß” or a “Personalausweis”, and you are not obliged to carry one of them with you all the time.
Windows is like a submarine. Open a window and serious problems will start.