In your dreams when you see a deceased family member and follow them, you will soon die and meet them in the afterlife.
My informant was told about this specific superstition when she was in high school. She states that a widow whom she knew saw her husband in her dream and soon passed away from an accident. She believes that this is due to how strong family bonds are in Korea; widows and family members are known to mourn their lost ones heavily in Korea, just like anywhere else. Thus she believes that family members usually follow their loved ones to the afterlife as they want to be with them. She also states that she tells this to her friends and family so that they do not have a similar fate.
I have a different take; I believe that this story is a way of moving on from your deceased family members per say. This story discourages people from sulking or being depressed about their family members for too long. It encourages people to live with the living and not think about the deceased. What is interesting about this myth is that it stays alive due to the connections that are made with people passing away after seeing their loved ones in their dreams. The only explanation for this is the fact that it has to be a strange coincidence.