For the amateurs out there, eating a good breakfast sandwich is like eating.....
Before digging in to the crunchy bagel, you need to nibble around the edges and eat the excess. If you have a natural casing sausage, scoring the top before cooking definitely helps make it easier to eat. Once you have the sandwich trimmed to the size of the bread, you gotta flip it so the top is down and the bottom is up. Easier to bite through the bottom of the bagel with top teeth and hold sandwich in place with bottom. A strong and nimble tongue definitely helps keep the spillage of the insides to a minimum. As SJ said, you use the bread to stop up any mess.
I had less than a forks worth of spillage on plate when I was done. Now, of course, eating at my house, there was no fork. It was a two finger pinch and in to the gullet.