Each timelapse can take a while to perfect, as you really need to visit the location first to see where the light will fall and work out your moves - what's going to be in the foreground, where are the changes going to occur, what's the likelihood of people walking or cars driving into shot, etc. Often you don't get the time to figure this out. Sometimes the equipment fails or your calculations are out and A LOT of time is wasted, sometimes the sun doesn't shine, sometimes there are too many clouds, and then every now and then you get lucky.

Music by Four Tet "Twenty Three" and sound fx courtesy of www.freesfx.co.uk