Miscommunication

The summer before I started as a student at Clemson, I worked as a lifeguard for a private company that supplied guards to various pools around the area that I live. About halfway through the summer my section of the company received a new supervisor.
One of the pools that I often was assigned to was an olympic size indoor pool at a k-12 grade school near my house. During the week we would have guards working alone covering different shifts throughout the various hours the pool was open for. During the weekend we would have 2 guards working together the whole day.
One weekend when the new supervisor was still new a lot of miscommunication must have occured because 3 guards showed up to work. We never quite found out why 3 guards were there that day, it was fun for us, but it certainly was not planned. We thought possibly that the supervisor got something mixed up but were not sure, so no one went home until we could contact the supervisor, which was several hours later.
When the supervisor realized what had happened he was a little upset because the boss was not to happy with him since they had to pay an extra person that weekend. He wondered why we all showed up for work that day but we all wondered why he put us all on the schedule for that day.
The aftermath was that the company lost a little money paying an extra guard, and we lost a little respect for our supervisor.
This problem occured because either the supervisor forgot to tell one of us we had the day off, or someone had missed the message that they were supposed to have the day off. All of this could have been avoided if the supervisor had properly checked the schedule and made sure everyone else knew what it was.