Can you believe your eyes?

Some years ago when the current writer worked as a consultant, We showed the image below to the directors of a construction company. So powerful was the illusion - that when it was shown on a projector (from a computer) they said we must have been cheating.
In the end I had to produce a version on paper for them to actually not believe what their eyes saw.

It is important to look twice at things.

Sometimes seeing is deceiving.

Are the squares A and B the same colour and tone EXACTLY? (This is not a trick question.)

Are they the same tone, colour, shade of grey?
The answer is - yes they are.

Our brains understand perspective, shading and light, and so makes adjustment to what we 'see'. In fact what we are seeing is simply a projection of our mind (occurring totally in the deep darkness of our brain).

We 'see' A and B as different when in point of fact they are the same. If you are unsure, print off the image - cut out the squares and compare them side by side without the chessboard context.

You will find it looks like the squares above (bottom right of picture).