Its all about perspective.  How we perceive something can be affected by what we see around it, or on it, or in it, or… I think you get the idea.  Take a look at the sign posts below.

The two poles are parallel.  Really they are! I know that you want to get a ruler to measure.  I bet you’re looking for a ruler right now.  Ok, go ahead, get the ruler….measure…now do you believe me?

Take a look at a smaller version of the same picture.

When the details of the picture are too small to notice,  the flag poles look parallel.  There are many details in the big picture that are meant to draw the eyes in a particular direction.  Starting from the bottom:

• The flags are on opposite sides of a small hill.
• The poles have a distinctive yellow and black candy stripe.
• The flags on the tops of the poles point in opposite directions.
• The left side of the drawing has a bluer sky than the right side.

All of these factors are meant to deceive your eyes making it look like the bottom is closer together than the top.  It is only when we shrink the drawing down to its basic geometric shapes, thus eliminating the finer details of the drawing do we see how the lines really relate to each other.