Sushi is now well-known as one of the representative Japanese foods. The slices of raw fish laid on slabs of vinegared rice can be savored at high class restaurants. How can people eat such food with their hands? Well, it may be high class fare now but, in the old days, it was Japan's equivalent of fast food and sold on open stalls. The custom of picking it up is a relic of those days. You are, of course, welcome to use chopsticks if you prefer.