The most common answer to this question is that the Swiss Army knife has two blades so that it can be used for both general purpose tasks and more specific, dedicated tasks. However, the reason for this design is actually much more complicated than that.
The Swiss Army knife was designed in the late 1800s by Karl Elsener, who was inspired by a folding pocket knife he saw while working in a cutlery workshop. He realized that a similar design could be useful for soldiers who needed a versatile tool that could be used for various purposes in the field.
Initially, the Swiss Army knife had only one blade, but Elsener soon realized that adding a second blade would make the tool even more versatile and useful. Thus, the now-iconic Swiss Army knife was born.
Interestingly, while most people assume that the two blades are meant for different purposes (one for general use and one for more specific tasks), they are actually both intended for general use. The main difference between them is simply their size; the smaller blade is better suited for delicate tasks while the larger blade is better suited for tougher jobs.
So there you have it: contrary to popular belief, there is no grand reason why the Swiss Army knife has two blades. It's simply a result of Karl Elsener's ingenuity and desire to create a truly versatile tool.