Thinking more about this, if you're running at a marathon, your concerned not with how far you've come, but how far is left. Such a view of life isn't likely to be very productive. I still think my point holds for your marathon effort -- 1 meter after start is very different from 2 meters after start (or say 50 and 100) -- however the difference between 1000m and 1001 (1050) -- not really easily perceptible without some kind of aid?