This is true because the leader sets the pace and the tone of the team. They watch and wait for the not so good moments to replay the same behaviors that the leader has displayed. It becomes a highly dysfunctional organization and those nasty little behavior spread like cancer that chokes the niceness out of the organization.
Every leader needs to check him or herself before reacting to anything in front of their employees. As we all know monkeys see and they sure in the heck will do what they have seen.