I think it's a risk issue. Which then becomes a potential liability issue. So if we ignore manufacturer's advice & get an infection, it's our fault for not following their instructions. Then it becomes a risk reduction exercise. So if we wash our hands properly before use, that reduces the risk of bacteria or gunk being transfered from our skin.. Which then leaves most of the risk being transfer from needle to finger, or stabbie device to needle & then finger. Those risks can then be reduced by keeping those bits clean.. Which is one reason why I like the FastClix pen. Most of the risk's in the cartridge & cap. One's throwaway, the rest is easy to clean.