<i>&quot;For example, a granny knot is much easier to undo, as its configuration of twists creates weaker forces within the knot. For centuries, sailors have observed such distinctions, choosing certain knots over others to secure vessels — largely by intuition and tradition.&quot;</i><p>This author does not know knots. Granny knots are weaker, but are generally harder to undo than a reef as they pinch themselves up, whereas a reef can be undone by holding both lines securely with their tails and just pushing, and it is the combination of how easy they are to undo after being under strain and the fact they lie flat, that makes the reef generally the preferred knot to the granny.