The mind is a remarkable thing, perhaps more remarkable than we dare imagine. Take, for example, this image. Which way is it turning? Clockwise or anti-clockwise? “Why, don't be silly,” I hear you saying, “Of course it's turning clockwise.” Ah... you must be right-handed.
You see it's actually not turning clockwise or anti-clockwise. It's an illusion. It will turn which ever way you want it to turn. Don't believe me, give it a try. As you're reading, slowly become aware of the shadow at the bottom of the image. Try to ignore the legs and just let your eye settle on the shadow and, presto, you'll see she begins to turn anti-clockwise.
Ah... the ambidextrous mind. Now, are you ready for a real challenge? Can you make her turn either way at will? That's a real test of mental strength. You can do it, the trick is in training your mind to recognise which leg she has extended. If her right leg is raised, she'd be turning clockwise. If her left leg is raised, she'll be turning anti-clockwise. It helps if you focus on the shadow again.
The funny thing is, it is harder to unlearn. Getting her to turn clockwise again is harder than getting her to turn anti-clockwise the first time. The mind loves a rut :)
Isn't it bizarre how you can literally talk your mind into seeing whatever you want to see? There's a lesson in there somewhere...