Why we count down to certain events

While visiting my brother and his wife they started a count down until they are done with their surgery rotation. It made me wonder why do we count down for a certain time. It seemed that we count down in order to realize the time that is passing to the upcoming date. If we see that time is moving it is easier to keep going, we don't feel like time is standing still if we have something visual to set time against, thus we have invented the countdown.

But why is it that we count down at all? Why do we want time to be always moving towards the future? Life seems to have more in the future, for more of us, than it does in the present. For my brother and his wife they are looking forward to their next rotation for school and don't particularlly like surgery so it makes sense that they want the future here and the present to be past. Thus, they have the stars on their celing to be pulled down every day so they can see the number of stars dwindle and realize how soon the future is.