Why is secondhand smoke deadlier than firsthand, as they say?

I guess because it affects more people maybe? I don't think you can really quantify it as has been said, the smoker is exposed to both. What people don't realize that it is heart disease that kills you before lung cancer ever will, and more people die of COPD than lung cancer as well. Ignoring the health risks, smoking makes you stink and stains your entire house yellow. Nothing good comes from it.