Common

Common sense is common to no one. A computer geek would never understand the common sense common to carpenters. So when you think everyone should know what you know ; you are the idiot. People brought up in New England do not have the common sense of someone brought up in a desert.

Walkin on a tin roof with Deck shoes is stupid regardless of your previous education. Luckily the ladder was secure enough to prevent a painful  reconnection to Mother Earth.