Sometimes the sole of your shoe falls off. Not so bad, kind of moccasin-like and soft. Nicer if it happens to both at the same time, so the ground is felt evenly.
Sometimes, though, it may happen that your dearest friend loses the sole to their shoe in similar terrain. Then you both rely on dampened duct tape, until the mud flapping can't go on. Then you may tie the sole to your tarp, and reunite sole to shoe at a later time.
What is a shoe without a sole? And a sole without shoe?