I struggled with this at first. The picture below appears to be spinning which way to you? Left or right? Ok. That was the easy part. Now convince ourself it is turning the other way. Really, go ahead an try.
Trust me on this...you can convince yourself it is spinning the other way, and when you do, it is hard to get back to your first way of perceiving it. If you are having trouble, focus a few inches away from the image and give it a moment or two in you peripheral vision. For me, I was convinced it was turning to the left (clockwise). I focused on a point a few inches to the left of my laptop screen and willed it to turn right...30 seconds later...it worked.
I'm not a huge fan of optical illusions, but I like being able to convince myself to perceive something in a completely different fashion. Way cool when you make it happen. Try it.