What actually "label.visble = true" did?

The code below is extracted from one of my project, it will hang when there a client is connected. When I make some changes in the showConnected() function, the program work well. I would like to know why!!


//The code below is at the main page

private void btOpenPort_Click(object sender, System.EventArgs e)
{
      Connector = new TcpServer(Int32.Parse(tbPort.Text), this);
      Thread runSrv = new Thread(new ThreadStart(Connector.OpenPort));
      runSrv.Start();
}

public void showConnected()
{
                //lbConnected is a label
      lbConnected.visible = true;
}

//These the code run is another thread

public TcpServer(int port, Server theBoss)
{
      PortNo = port;
      boss = theBoss;
}

public void OpenPort()
{
      Listener = new TcpListener(PortNo);;
      Listener.Start();
                  
                  
      Socket ConnectionSocket;
      NetworkStream socketStream;
      BinaryReader reader;
      BinaryWriter writer;

      while(!programClosed)
      {
            ConnectionSocket = Listener.AcceptSocket();
                        
            boss.showConnected();
                        
            socketStream = new NetworkStream(ConnectionSocket);

            writer = new BinaryWriter(socketStream);
            reader = new BinaryReader(socketStream);
            ClientReader = reader;
      }
}


When I initially set the visible of lbConnected.visible = false and lbConnected.Text = "" and modified the showConnected function as below, the program work well, why?

public void showConnected()
{
      lbConnected.Text = "Client Connected !!";
}