Simple put, John can run 100 meters as fast as George can run 90 meters. If John starts 10 meters behind George, they will meet at 90 meters, because George will have ran 90 meters but John will have run 100 meters (remember he began 10 meters behind George).

So the race will be for the final 10 meters. But John runs faster than George, so he will eventually win.

Now take it a step further. What will be the difference between John and George when John wins the race at 100 meters?