When introducing students to the preflight check, I always tell them that some previous pilot may have damaged the aircraft and failed to notify anyone, so their job is to find the damage. I also relate an article from many years ago in the crash comic, of a part owner of a C180, the other part owner had removed the rudder and failed to to advise him, he managed to get airborn with tragic results. That seems to get the message across. Its no good finding the fault once airborn. Cheers Q