More than a century ago, Albert Einstein’s celebrated theory of relativity altered the world’s understanding of space and time. This week, the wild-haired physicist’s far-simpler “theory of happiness,” imparted to a bellboy, fetched more than $1.5 million at an auction in Jerusalem.

In 1922, Einstein was at the Imperial Hotel in Tokyo, where he was on a lecture tour, and had recently learned that he had won the Nobel Prize. When a bellboy delivered a message to the physicist, he fished in his pocket for some change to tip him and came up empty.

Instead, Einstein offered a tip in the form of his theory on how to have a happy life.

“A calm and modest life brings more happiness than the pursuit of success combined with constant restlessness,” he wrote in German on a piece of hotel stationery.

On a second sheet, he wrote, “Where there’s a will, there’s a way.”

Einstein told the bellboy, according to the auction house, that if he was lucky, the notes might become more valuable than a regular tip. His words, befitting a man who had transformed our comprehension of the universe, were prophetic.