For many years, Mothers have chosen this way to help their children to remember something.
This is a carry-over from olden days when people tied pieces of cloth around any painful part of their body.
This cloth was tied in one area to keep the “spirit of life” in that area, and so cure it and keep the pain from spreading to other parts of the body. The string on the finger was designed to “keep” the thought there, to be remembered later when it was needed.
