As a pre-med student at Washington University in St. Louis, I had to take a difficult class in physics. One day our professor was discussing a particularly complicated concept. A student rudely interrupted to ask, "Why do we have to learn this stuff?"
"To save lives." The professor responded quickly and continued the lecture.

A few minutes later, the same student spoke up again. "So how does physics save lives?" he persisted.

"It usually keeps the idiots like you out of medical school," replied the professor.