Look at it like this: Lets say you work on a pig farm scooping up shit all day. When you first get there, yeah, it smells, but day after day, you start not to notice it as much anymore. You take a city boy and put him in the pigpen, you bet he's going to smell that shit!

It's because you are used to the smell and don't notice it anymore. Like someone who smokes tobacco. They don't even know how much they smell because they are used to it, but take a non-smoker and you can smell it on their clothes several feet away.

So yeah. Another one of lifes greatest mysteries, huh.