Ever looked at a "Magic Eye" book? I find them almost irresistible.
Here's the deal, for those who've never done it: the book is filled with pages of tightly packed images, repeating graphic designs. These can be anything from discernible shapes such as dogs or kites, repeated across the page to more amorphous shapes, less recognizable and densely packed. The pages themselves have nothing specific to focus on and can seem unsatisfying.
The technique is the thing. You select a page, and hold the book up to your face, with good light behind you but no shadow. Your nose needs to touch the page at first. Focus your eyes at a place on the page and once you feel "fastened on" start moving the book away. Don't let your focus wander. You will feel a bit of a pull on your eyes and soon see extra shapes develop. As you get the book about an arms length away or a little less, you will see three dimensional objects emerge. The page is called an autostereogram, and you don't need fancy equipment to see in stereo. In the gentler versions they are a wonderful treat. In some of the more intense ones, the pictures may be odder and more thought provoking.
This is complex science AND great fun. For more information about the science see: http://en.wikipedia.org/wiki/Autostereogram
For people who are newly acquiring the skill of 'Magic Eye," that first 3D emergence can be quite fun - triumph of imagination over logic.
Some people find it difficult to do. We could ask all sorts of questions about that - do they lack imagination? Are they not patient enough? Do they have an eye problem that prevents them? Are the maybe too logical or analytical?
I do think you have to let yourself believe. I think you have to let go of what you assume and have the eager anticipation that something wonderful (or weird) is coming.
Do try it! Even you cautious serious types. Let your brain do something unusual, stretch its legs, and exercise its magnificent and marvelous capacity.