On 19 December 1991 the Federal Labor Court decided a case about musicians of the Deutsche Oper Berlin. The dispute was about pay for a short strike. In its reasoning the court described the duty of an orchestra musician. To perform his services properly, he needs individuelle Vorbereitung durch häusliches Proben und Üben, individual preparation by rehearsing and practicing at home, in order to meet the orchestra’s quality standard. The collective agreement did not say this anywhere. According to the court, the parties to the agreement took it for granted, selbstverständlich.