Author Dr. Seuss wrote the book "Green Eggs and Ham" because the editor made him a bet that he could not write a book, which contained less than fifty words.

Bet You Wouldn't Eat Them

Actually, green eggs and ham is a traditional American dish that involves cooking the eggs with spinach or other green vegetables, which color the eggs, and then serving it with regular ham. But in his famous poem/book, Dr. Seuss turned the everyday dish into something horrible to contemplate- eggs that were actually green with green yolks and served with ham. Who would eat that stuff?

Certainly not the narrator of the book, who complained about the awful stuff to Sam-I-Am. Nor likely, Seuss himself. But he had a better reason than an unusual meal, to write the book.

Bennett Cerf, who was Seuss' publisher, had bet him $50 that he could not write a book, using only 50 different words. He was prompted to dare the author, after publishing Seuss' "Cat in the Hat", in which he used only 220 different words.  

What resulted was a book for young readers, which used exactly 50 different words, in a story style known as "cumulative", which meant that the longer it went on, the more details were added. 

Not only did Seuss win the bet, but he did it in fine style, using both iambic and trochaic pentameter. There is no record of whether Cerf paid up.