YSK what a granny knot is

Why YSK: The granny knot is the most common reason as to why show laces seem to be undone so easily. It's caused when the Starting Knot & Finishing Bow don't “balance” each other. Recognizing this can help you make your shoe knots much more secure.

Edit: (BTW, YSK the website as well. It's a really good resource for tying and lacing shoes)