Explain why positive reinforcement is more effective than punishment over the long run.

Punishment (by definition) trains an employee in what not to do, not in what to do. Therefore, a leader must specify an alternative behavior to the employee. When the employee performs the desired alternative behavior, the leader must then reinforce that behavior positively.
A criticism for using punishment is the chance that it will have negative effects, especially over long or sustained periods of time. Punishment stops an undesirable employee behavior. However, the potential negative consequences may be greater than the original undesirable behavior.