The Ford 5.4 L engine is the perfect storm of poor engineering. The heads and combustion chamber are poorly designed, enabling carbon to build near the spark plug holes. The spark plugs are poorly designed and have a two piece design; the lower part of the plug which sticks into the combustion chamber, gets surrounded by carbon. The carbon clamps onto the spark plug and when you remove the plug that bottom part stays in the combustion area, held by the carbon. 

Over the years we have come up with a variety of tools and procedures to remove the plugs. The main idea is to reduce the amount of carbon in the combustion area so the plugs will release and come out without breaking. Some times it works, sometimes it doesn’t. There is a special tool designed to pull the remnants of the of the old plug out of the combustion chamber. 

In typical Ford fashion, instead of fixing the problem they create a work around… that really isn’t.

You can see from the picture how the bottom part of the spark plug separates from the main part… and stays in the combustion chamber.