George Dantzig was a PhD student at UC Berkeley.
One day he walked into statistics class a bit late, after the professor had started lecturing. He saw that there were two problems written on the board, so he wrote down the homework then started taking notes.
He worked on the homework problems for the next few days. He knew he was going to be late, but the questions seemed a little harder than usual, so there wasn’t much he could do to speed up.
Finally, after a few days, he was done. He went to his professor and apologized for taking so long to do the homework, asking if he still wanted it. The professor said to just leave it on his desk.
A few weeks later, George woke up to someone banging on his front door. He opened it and was surprised to see his professor looking strangely excited.
He had no idea what was going on until the professor explained that the problems George copied from the board were not homework, but actually two unsolved problems in statistics. And he had solved them.