Once the ballet has been choreographed or staged and the dancers all know their parts it is time for them to rehearse and clean their parts. The dancers will go over parts of the ballet hundreds of times until it is as close to perfect as possible. As they keep repeating dances they will get corrections given to them by the ballet masters, and the choreographers, (who are quite often the same people), and they will be coached on their dramatic expression by the director. This is the longest and hardest part of creating a ballet because the dancers have to keep repeating the same thing over and over again and every time give one hundred percent as if they are performing. Also, if it is a ballet with a story it is a dramatic challenge for the dancers because each event has to look like they have never seen the event before and they didn't know it was going to happen. Otherwise it looks "staged" and the audience gets bored.