Suppose you are in a rush to get down a long terminal at an airport. Part of the terminal has moving walkways installed, and part does not. Sometime during your trip down the terminal, you need to stop to tie your shoe. Will you get to the end faster if you tie your shoe on the moving walkway, on the normal part, or no difference?
Now imagine that as you traverse the walkway, you will run some of the time. However, you only have enough energy to run for a set amount of time. Should you do your running on the moving walkways, the normal part, or no difference? (Ignore practical matters such as the need to tie your shoe right away to keep from falling, the possibility of pacing your running, etc.)
Now, if you know relativity, imagine that you and the walkway may be moving at relativistic speeds and re-analyze the situation. Note that the time on the airport clocks may be different from the time on your wristwatch.