"You find that most people place one half knot on top of another. This results in either a notoriously unstable granny knot or a very stable reef knot, depending on whether the two half-knots have the same or opposite orientation," Dr Polster said. "If you are a granny-knot person, you can turn yourself into a reef-knot person by changing the orientation of one of the half-knots."
Important scientific investigation reveals how to tie your shoe laces properly. The Guardian explains.