What colour has the word black and the word white in this image? The question brings your mind in a twist, a state of cognitive dissonance. You see black where the answer should be white and v.v.

Cognitive dissonance is the mental discomfort (psychological stress) experienced by a person who simultaneously holds two or more contradictory beliefs, ideas, or values.
This discomfort is triggered by a situation in which a belief of a person clashes with new evidence perceived by that person.

When confronted with a situation like this people will find a way to resolve the contradiction in order to reduce their discomfort
A psychic mechanism then comes into play to eliminate the tension by bringing the ideas into line with each other, thus restoring the peace of mind, for instance:
"Luc turned this image negative, he is a fool to do so, it's ugly and bad taste."

Cognitive dissonance can be a driving force to develop new ideas, but can also lead people to shut themselves off for information that refutes their beliefs.
When you’re familiar with this phenomena you’ll see that the world is full of it …….

For some peace of mind, here's the "normal" image: