When you hold a new Güde knife in your hands, it is a very sharp tool. But the more you use the knife, the more it loses its sharpness. This is the case with all classic knives. That's why knives need the sharpening steel.
Faced with the choice of having a complete knife series but no sharpening steel, or a single knife with a sharpening steel, a more experienced professional will always opt for the second alternative. Because without a sharpening steel, the best knife is useless.