Say, you are in a cafeteria.

You are putting salad, soup, pasta, dessert, and soda on your tray. When you are about to make a payment and lift the tray with one hand, and look for your wallet on the other hand -- suddenly, you lose your balance --> the tray tilts --> the dishes slide down --> collapse!

This particular soba restaurant's employees must have witnessed similar tilting-incidents in the past, and they came up with a nice and simple solution.