Egg of Columbus
Some guests of a Spanish nobleman, thinking to lessen the merits of Christopher Columbus’s discovery, declared that the thing itself was easy of accomplishment - all that was necessary was to have the thought in the first place. Without deigning to reply directly to his detractors, the great navigator called for an egg and passed it among the guests, asking them to make it stand on end. None of them being able to do so, Columbus took the egg and, breaking the end gently, caused it to stand upright on the plate. The assembled guests with one voice exclaimed that this was a simple thing to do. “Yes”, replied Columbus, with a smile, “the only thing necessary was to have thought of it!”
The expression “the Egg of Columbus" has since passed into a proverb, meaning anything that one cannot do and yet finds extremely simple on being shown.
5000 Facts and Fancies by William Henry P. Phyfe, 1901.