Proper planning will get you far, but sometimes life happens, and you'll need a plan B. Think about some of the variables in your life that could affect your ability to arrive on time for work. Sick children, traffic, car breakdowns... the list goes on. It may not be possible for everything to work out so smoothly, getting your shift covered or still making it to work on time. Your interviewer is looking to see that you are proactive and that you can handle the stress of unexpected situations that can arise.