Your Shoe is Untied
I ran across a fantastic volume called The Ashley Book of Knots by Clifford Ashley. Ashley himself is a fascinating person worthy of separate discussion but his book was the key to my cure.
It turns out that Ashley has no solution at all for tying shoelaces. "Shoelaces" appears in the index but he only writes about lacing shoes. Among the literally thousands of knots documented in the book, however, is the common reef knot (also called the square knot.) The reef knot gets its name from its use. You have probably heard the expression "reef the sails". "Reefing" is rolling up a sail to some extent to reduce its effective area. When you reef a sail you have to tie it in place. The reef knot is used there. It has the property of being very secure unless you pull one of the loose ends across the knot which causes the knot to "capsize", or "spill" and come undone. You can see how this is useful on a reefed sail.
A reef knot is quite simply tied. Take a half knot (the first step most people take in shoe tying) and then take another half knot in the opposite direction on top of the first. If you take the second in the same direction, you get a granny knot which, being frictionally unbalanced, will not stay tied.
By now you may be starting to twig to the problem. It turns out that the common bow tied in a shoelace is a reef knot taken with two bights (loops in the rope) which is called a "slipped reef knot". So, very simply, if you try to tie a slipped reef knot in your shoelace and you end up with a slipped granny knot, it will come undone. So how to fix it?
Here is the secret to tying your shoes just once each time you put them on: reverse the direction of the first half knot you make. If you normally put the left over and right under, put the right over and the left under, and vice versa. Then, proceed to tie as usual. It's that simple. It will save you time, embarrassment and for some, pain. It will eliminate the ugly, dubious "double knot". Double knotting is completely unnecessary. The shoes stay tied and they look nicer.
In researching this post I ran across a site from which I got the picture, above: Ian's Shoelace Site. The site is wonderful. It covers this topic, lacing, tying (17 knots!), and many other shoelace-related areas. It is a great place for advanced shoelace studies or to see pictures of what I am talking about if you can't understand my description.
In our correspondence Ian and I agreed our independent, informal visual surveys indicate about 40% of people suffer from Granny Syndrome. Once you figure it out you might just find yourself mentioning it to friends when you spot their telltale parallel bights.