Simplicity.

Take a picture of a glass,
turn the camera out of focus and use a distorting lens.
Then ask people, "What's that?"
They will answer, "it's a picture of a glass."

;

Take another picture of the same glass.
Don't put it out of focus and don't distort it.
Make it normal.
Then ask people, "What's that?"
They will answer, "It's a glass."

----------------------------------------------------------------------------
All credits go to "Whatever You Think, Think The Opposite" by Paul Arden.