Strafe muss sein
Strafe muss sein (old spelling: Strafe muß sein) is a German saying that means "punishment is necessary (inevitable)" (or "there has to be punishment").
This phrase, or proverb, roughly carries the same meaning as Spare the rod and spoil the child, but is used much more often than the German equivalents Spare die Rute und verdirb das Kind or An der Rute sparen rächt sich noch nach Jahren.
The phrase refers to the necessity of punishment in general, not specifically to corporal punishment or spanking. This may be one of the reasons why it is still in common use. Strafe muss sein is typically said by a parent or other authority figure to explain to a child who has commited a serious offense why they can't be let off with a warning, but have to be punished. The phrase implicitly expresses that the parent may not like to punish the child, but sees punishment as inevitable in the given circimstances.
The phrase is also used by children themselves, and by adults in other contexts.