Varicose veins are the result of an improper selection of grandparents.

In this wry aphorism, Osler reduces a common medical complaint to heredity: you cannot “choose” your ancestors, so some conditions are essentially inherited bad luck. The joke also reflects a clinician’s habit of looking past symptoms to underlying causes—here, the predisposing weakness of venous valves and vessel walls that can run in families. More broadly, it pokes fun at the human desire to assign blame or find a simple fix for chronic ailments; sometimes the most important “cause” lies outside personal control. The line’s humor makes a sober point about constitutional factors in disease and the limits of medicine and lifestyle in preventing every condition.