The Avianca crash comes to mind. The crew said they're low on fuel or something like that, but continued to accept ATC vectors. They were pilloried for not declaring an emergency and out of the accident came the silly "minimum fuel" concept. The crew should have been pilloried for not getting the damn thing on the ground before they ran out of gas. "Declaring" an emergency would only have punted the outcome to ATC. IMO, the emphasis in teaching should be to DO what's required, not SAY what really isn't.