Time is a river, and we are the salmons

in

Time has been often compared to a river, because it flows. But in which direction? Consider this: things that were once in the future will soon be past. So from our reference point, time flows in the reverse direction! And that makes us creatures that swim upstream :-)

Or, as U2 puts it in Zoo Station (from Achtung Baby):

Time is a train
Makes the future the past
Leaves you standing in the station
Your face pressed up against the glass