Dutch and German are classified differently (cat 1 vs 2). But it is a well-known language gimmick of these 2 specific languages that when a native speaker of

Dutch and German are classified differently (cat 1 vs 2). But it is a well-known language gimmick of these 2 specific languages that when a native speaker of one of these languages speaks slow enough, a native speaker of the other one can understand him reasonably well. So where do these 6 weeks of extra work come from?