Imagine that a man named Robinson Crusoe lives on a deserted island. His main source of food is coconuts. He works for most of his day shimmying up trees to get coconuts to eat. One day he thinks of a new invention—a coconut picker. He ties some long pieces of bamboo together with a rock at the end to knock down the coconuts. Now he no longer has to spend hours climbing trees to reach the coconuts. He gets twice as many coconuts a day and has more free time to work on building a boat to escape the island. His poor health also improves somewhat, with fewer climbing injuries and more calories in his daily diet. 

What important lesson about economic growth is illustrated by the invention of the coconut picker in the story?