Grouping

The neatly assembled box on the right contains the same components as the scattered group on the left. Which one do you find more appealing?

Similarity

Note the similar triangle shapes here. The individual similar elements create something much more specific and meaningful.

Ground

Do you see two faces or a goblet? I'll leave you to ponder the psychoanalytical implications of your response...

Closure

We are programmed to see things as whole when they may not be. The lines on the top of this panda's back are not drawn, but it doesn't stop our busy minds from establishing parameters that give the image meaning.

Space

The creator of this piece simply cut a swath through the S, P, A, C, and E of this graphic leading to the star. Do we see the slice in any of the letters individually? No. Instead, our minds assign motion to the star.

Symmetry

Although this color wheel is just an assemblage of sail-looking triangles, the orientation of each of them in a cyclical pattern lends the impression that they are part of a unified whole. I mean come on, look at that cool black sun in the middle!