Your interviewer knows you're not perfect. It may seem as though they are digging for weaknesses, when in actuality they are interested in your ability to learn from your mistakes.

"I didn't check the work schedule for the next week and accidentally did not show up for work on a day I was scheduled. As soon as I got the phone call I started getting ready for work. Even though I was four hours late, I apologized and then got straight to work. Now I check the schedule every week and I keep a copy of it as well. I strive to be reliable and I never miss a day."

When you talk about the mistake, focus on what you did to correct it and how you learned from it.