Why Should Swing GUI Code Be Placed On EDT

According to what I read, "when programming in Swing, your GUI creation code should be placed on the Event Dispatch Thread (EDT). This will prevent potential race conditions that could lead to deadlock." (See below for code.)

Why is this? How could making a GUI lead to deadlock?

public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}