The year 1939. Place: University of California at Berkeley, California.
The student was very late to his math class. Almost half the lecture was over. He sat down quietly and took notes. He noticed the professor has written 3 problems on the black board. Since he was late coming in, he was afraid to ask the professor about them. He just assumed they were the home work assignment the professor had given to the students.
He copied those 3 problems in his note book. Went home. Started to work on those 3 math problems. He found them very very difficult. Worked whole night solving those 3 math problems. Finally, during the early morning hour, he solved all those 3 problems.
Went to the class next day. Gave his home work assignment to the professor. He told the professor how difficult those 3 math problems were and how he worked on them the whole night and solved them finally.
The professor immediately jumped out of his chair and asked: WHAT? WHAT DID YOU DO? The student explained how he worked the whole night and solved those 3 difficult home work assignment.
The professor explained that they were not home work assignment. Since he was late to the class the previous day, the student was not present when the professor put them on the black board. The professor explained those were the 3 mathematical problems that were unsolved by anyone. The student mistook them for home work assignment and solved those 3 unsolved math problems.
The professor published his "home work" and he was given credit for that. The professor also recommended a Ph.D for him.
That student was George Dantzig.
PS: If you Google his name, you can read several versions for this incident.