Work Miscommunication

One time when I worked at the YMCA, I was scheduled to work a Saturday morning shift, but I got somebody to cover it because I was not going to be in town. It turns out they thought they were not working until the following Saturday, so they never ended up coming in for me. Neither of us showed up for the shift, so they had to call the "on-call" person to cover it. It could have been prevented if I would have written down the correct date on the calendar that this person was working for me and made sure they were aware of the day they had to come in as well.