From Wikipedia—-
The objective in employing such a bridge, constructed according to Zen philosophy and teachings, is to focus the walker's attention to the mindfulness of the current place and time moment - "being here, now". As it often has no railings, it is quite possible for an inattentive walker to simply fall off an end into the water.
The zig-zag of paths and bridges also follows a principle of Chinese Feng Shui.