Man can live for about forty days without food, and about three days without water, about eight minutes without air ... but only for one second without
In black you can read the word GOOD, in white the word EVIL (inside each black letter is a white letter). It's all very philosophical too, because it visualises the concept that good can't exist whithout evil (or the absence of good is evil ).
Can you see why this painting is called optical illusion ? You may not see it at first, but the white spaces read the word optical, the blue landscape reads the word illusion. See for yourself !