Thinking Outside the Box
"The expression "thinking outside the box" is thought to come from the puzzle below. The idea is to try and join up all the dots using four straight lines or fewer without taking your pen off the paper or tracing over the same line twice.
The 'box' that the expression refers to is the implicit one formed in your mind by the dots. To get the solution you have to ignore this implicit box: you have to, as it were, think outside it. via: http://goo.gl/zwOHv