“If you shake your leg when you’re sitting, you shake off all your good luck.”

My informant comes from a Korean family. She had no idea why she was taught this as a child, but recalled her mother being adamant about the dangers of shaking one’s leg (she demonstrated – the saying seems to apply to when one is sitting with one leg crossed over the other, jiggling the foot of the leg on top). There could be some sort of superstition involved in this belief; however, I think it’s likely that people simply wanted their children to stop fidgeting and made up a reason for them to refrain.