The story goes:

Whilst a chap was at his girlfriend's parents for dinner one night, he noted that his girlfriend chopped off each end of the roast before placing it in the roasting dish to cook the roast.

Peaking his interest, he enquired “Why did you chop a centimetre off each end?" and the reply was “My mother always does it that way". His girlfriend's mother happened to be in the other room, so the chap promptly went and asked “When you cook your roasts, why do you cut a centimetre off each end"? The reply was “Because my mother always did that".

Her mother happened to be in the room and over heard this story and said “Well the reason for that was because my roasting dish was only quite small and I had to cut off each end so that the roast would fit".

The moral of the story, just because it has always been that way, doesn't mean that it is right!