Why is it important for leaders to be in control of their attitude?
Leaders should lead by example as much as possible. The attitude "do as I say, not as I do" doesn't fly far with most people. If leaders expect those they lead to act appropriately, they must do so first.
So the people of their country don't overthrow them.
You wouldnt want that attitude to rub off on the people you are leading, now you got problems