It was the last day of the final examination in a college. On the steps of the teaching building, a group of engineering students were waiting for the last exam, about which they seemed quite confident. They thought the exam would be easy, because the professor had said they could bring with them any books or notes during the test. Right after they came into the classroom. The professor handed out the papers, on which there were only five questions. Three hours passed. The professor began to collect the papers. The students no longer looked confident. On their faces was a nervous expression. The professor watched the worried faces before him, and then asked, "How many of you have completed all the five questions?" No hand was raised. "How many of you have answered four?" Still no hands. "There? Two?" The students moved restlessly in their seats. "One, then? Certainly somebody has finished one." But the class kept silent. The professor said, "That is exactly what I have expected. I just want to make you know clearly that even though you have competed four years of engineering study, there are still many things about the subject you don’t know. These questions you could not answer are common in everyday practice." Then, smiling, he added, "You will all pass this course, your education had just begun." The years have obscured the name of this professor, but not the lesson he taught.