Belly Button Lint

This is just one of those great mysteries of life. I've never really had a belly button lint problem. I've only had it a few times in my life. However, I once had a roommate, who shall go unnamed, who had to pick a big nugget of lint out of his belly button about twice a day. But where does it come from? The prevailing theory is that it comes from rubbing fuzz off the inside of your shirt. But if that's the case, why doesn't everyone get it? There are all kinds of other variables that must come into play like the amount your stomach sticks out, chest hair, fabric of the shirt, etc., but it still makes no sense. Can anyone answer this vexing question? My own belief is that there is a lint monster who, tooth fairy-esque, goes around and puts lint in the belly buttons of bad boys and girls.