Because

“A little girl watched her mother prepare a roast for dinner. Before putting it into the pan, her mother chopped off a small piece on the end of the roast. The little girl asked her why and the answer was, “Because that's the way my mom always did it”. So the little girl went to her grandmother and asked why she chopped off the end of the roast before putting it into the pan, and the answer again was “Because that's the way my mom always did it”. Finally the little girl went to her great-grandmother and asked her why she always cut off the end of the roast before putting it into the pan, and the answer was “Because that's the only way it would fit the pan”.