Most people will find that their eyes automatically group a number of these circles together to make patterns.
Explanation
In this optical illusion, you may see the small circles form patterns. The eyes constantly look for patterns in what they see. They would rather categorize a bunch of small circles as a pentagram or a diamond than have to deal with identifying each dot independently. By doing this, the brain frees up part of itself to look for other things that may be of interest.