Can You See All the Dots in This Picture? Nope. You Can’t.

Optical illusions are great ways to kill time at work without actually working. Here's why this particular one works.

According an article at MSN.com, it's because:

humans have pretty bad peripheral vision. If you focus on a word in the center of this line you’ll probably see it clearly. But if you try to read the words at either end without moving your eyes, they most likely look blurry. As a result, the brain has to make its best guess about what’s most likely to be going on in the fuzzy periphery — and fill in the mental image accordingly.

with this regular pattern of gray lines on a white background, the brain guesses that there’ll just be more of the same, missing the intermittent black dots. Those dots disappear and reappear as your eye jitters around.

And now you know.