In ancient times, when the human mind still struggled to grasp the idea of exponential growth, there was an old Persian tale. Once, a clever courtier presented his king with a chessboard.

“How shall I reward you?” asked the king. “My noble lord,” said the courtier, “I ask for nothing but this: fill the chessboard with rice. Place a single grain on the first square, and on every square after it twice as many as the square before — two on the second, four on the third, and so on to the end.”

The king was surprised. “Such a modest request shows how honorable you are.” And how much rice would it come to? The king had probably pictured a small sack. In truth, he would have had to pour out more rice than is grown in all the world.

The lesson: when it comes to rates of growth, do not trust your intuition — because you simply have no feel for them, and the sooner you admit it, the better. What will actually help you is a calculator, or the simple trick of estimating the doubling time for small rates of growth.

— Rolf Dobelli, “The Art of Thinking Clearly”