"Using a slow-motion camera and a series of experiments, mechanical engineers at University California Berkley found "shoelace knot failure" happens in a matter of seconds, triggered by a complex interaction of forces." Scientists, eh - how could we manage without them? 'shoelace knot failure' http://www.bbc.co.uk/news/science-environment-39573642
Let me guess: it involves a complex interaction of guns, global warming and misogyny. Oh, and hate speech. Almost forgot that one.
Close but I think it's from vibrations caused by Al Gore and Michael Moore walking together. University of Berkley?
They become untied because of either poor knot tying and/or poor shoelace design. Better running shoes have superior laces that stay tied.