The latch on the left is correctly installed. See how only the main portion, the larger part goes through the strike plate. Now you can see on the right side that both pieces are going into and through the strike plate. This is the wrong way. Why is this? When the smaller metal piece is prevented from going through the strike plate and instead presses on the strike plate, it prevents the larger latch from being pushed back. That pushing back of the latch is exactly how a bugler can get through a lock. So if the smaller piece is installed properly then the larger piece can not be forced back. It's an amazing thing. it's such a small difference but it can make all the difference.