It's not a myth, rather it is an optical illusion. Many people watching it will not see a loop because their eyes, and their brain, aren't able to see the loop. It does engage your brain it right hemispherical reaction as well as left. Many tests like this are used in epilepsy research.

For a "hack" of this, cover the girls body and only leave her foot visible. You will see that you can change the directions as the stimuli has been reduced. So unless, for me, it's on a loop every 5 seconds... I'd say the myth is a myth.

For another test on this that isn't a "myth", use your dominant hand and write the number 8. Have your foot on the same side "write" the number as well. You will see that for most of us, it is impossible to continue with your foot while writing a perfect 8 as both sides of your brain are trying to compensate for directions and reactions.