There was once a physics professor who used to be a cross country athlete in college. He still ran marathons for leisure, and was fast enough to win his age group at the Boston Marathon each year. On the day of his first lecture each semester, he would challenge his students to do lots of physics exercises throughout the year so they would be ready for the exams. “Or,” he would say, “you may challenge me to a marathon on the day before the exam. If you win, I’ll give you an A in the class.” Most students would think about this for a moment before realizing they could never beat the professor’s time, even if they trained tirelessly for the whole semester. So they’d grudgingly resolve to study hard instead.
But one semester there was a student who was a star on the college’s cross country team himself. He saw an opportunity to kill two birds with one stone–by training for his sport diligently, he could free himself from the obligation to study for his hardest class. So he trained all semester with the goal of peaking at exam time, so that his marathon time would be well below the professor’s best published time for the Boston Marathon. At the end of the semester, he challenged the professor to a marathon. He won by only the slimmest of margins, because racing together pushed both athletes to put in personal record performances, but his more focused training won out.
As they recovered afterward, the professor thanked the student for a sporting race and wished him well at the exam the following day.
The student protested. “But you said you’d give me an A in the class if I beat you!” The professor just laughed.
“Oh, that? Son, the university would never stand for it. We have a lot of money riding on our reputation for producing well-trained physics graduates, and you’d never pass another class if you didn’t understand the material in this one.”
“But I spent all semester training because I thought I wouldn’t have to take the exam,” the student said. “I’ll sue you for fraud!”
“It’s just something I say to get students to compare studying physics with training for a marathon in their heads,” the professor said. “It wasn’t written in the syllabus and you’d be laughed out of the ombudsman’s office. You’re an adult now, you should already be able to recognize when something you’re told is too good to be true. We didn’t get to the moon by shooting for the stars, we got there by shooting for the moon with extreme specificity.”
“So you’re saying I’m going to fail just because I believed your lie? How are you going to compensate me for this?”
“A guy like you who’s knuckleheadedly stubborn enough to beat me in a marathon wasn’t going to learn this any other way,” the professor said. “Consider it a relatively cheap life lesson and be thankful you paid for it with nothing worse than a bad grade.”
Then the student had to make a choice. So he decided to cut his losses by learning the lesson and retook the class over the summer. As a distance runner he was accustomed to hard work and discipline, so he had no trouble earning an A by applying his efforts to the right thing. And when he became an accomplished physicist later in life, anytime someone would suggest a project that would “kill two birds with one stone” he would quietly work to make sure they wouldn’t be in charge of anything important.