The rule is much older than the dining rooms people learned it in, and none of its original reasons survive. It appears to have taken hold in medieval England for practical reasons: feast tables were often boards laid across trestles rather than fixed furniture, so a diner leaning hard on one could tip it over; guests were seated close enough that a planted elbow pushed into a neighbour's space and knocked plates and glasses; and long sleeves resting on the table trailed into the food. By the seventeenth century the objection had become aesthetic rather than structural. The conduct book 'A Gentlewoman's Companion' described elbows on the table as a 'ravenous gesture' (the posture of someone too hungry to behave), and nineteenth-century etiquette writing aimed the rule particularly at women. Modern tables do not collapse. What is left is the association with greed and slouching, which is why people taught the rule still flinch at it and people who were not taught it cannot see the problem.