Originally Posted By: TeacherRO
"One is none, two is one"

Yet I never see the instructors who advocate this saying with two backpacks or two sleeping bags...

Yep. Those bromides make sense if you don't think about them.

You run into the same sort of problems with some people who "teach" gun safety who repeat "treat every gun as if it is loaded at all times" again and again.

(You shouldn't clean a loaded gun, so how exactly do you clean a gun if you treat it as loaded?)