If one person commits a crime and is defined a criminal then society may react to that person as a criminal. This will in turn require him to act as a criminal. The is not seen as a criminal and as such is not required to be a criminal in return. Labeling theory relies on the ideas of primary and secondary deviance. Primary deviance is when someone commits a crime.
Secondary deviance is when someone is labeled a criminal and so acts in chracter with the label.
According to secondary deviance the more someone is defined as a criminal the more likley they will commit a crime. If labeling theory is correct then the way to lower the crime rate is found in changing how society interacts with criminals to avoid labels.