The righthand image is recognized almost immediately. Even though the illustration consists only of three lines that are not even connected, our mind immediately recognizes the letter. An illiterate wouldn't be able to recognize the image, but we can recall saved visual information, ammend the missing lines and "see" the character.

This law should be kept in mind when designing a new logo. If previous knowledge of some kind is necessary to understand a logo, it could be ominous - for example if the logo is used internationally. Other cultures could be lacking this knowledge, so the logo might not be understood.