I receive a bunch of questions in reference to my 1080P Does Matter article. Some of the questions are along the lines of "Do I really lose the benefits of 1080p if I sit too far away from a small screen? How? The lines of resolution don't go away." While the lines are still there, you're eye can't detect them, but I haven't found a simple way to explain this. Then I came across this article and picture (via digg) that demonstrate a great, simple-to-explain example.

quoting http://bloggerwhale.blogspot.com/2007/03/dont-trust-your-eyes.html#
In the pic below you can see two faces. A normal face on the right and a wicked one on the left. Now get up from your chair and walk some 8 steps back and see the magic. The two faces interchange their positions.

This is a great example of when you can perceive the available resolution and when you can't. Up close, the fine lines (wrinkles) in the left picture are very apparent, but become smooth as you back away; the shadows under the squinted eyes look like the eyes. The fine lines defining the lips and eyes in the right picture become less apparent with distance and the shadows below the mouth become the mouth; the shadows above the eyes become part of the eyes.

To summarize, pretend you're viewing this picture on a HDTV and the picture and screen resolution is 1920×1080. You're getting the full benefit of 1080p if you sit close enough to your TV to see a wicked face on the left and normal face on the right. If you sit far enough away that you see a normal face on the left and a wicked face on the right, you could go with a lower resolution TV.