Guy at the Gary job taught me to check the firebox before signing off, saved me a callback
He handed me his 40 year old flashlight and said "look up, everybody looks down." I found a crack the size of a hair that three other guys missed, and now I always check the crown sheet first.
How many of those old timers actually teach that stuff anymore though? Feels like the flashlight trick only gets passed down if you happen to work with the right guy.