think outside the box
The phrase think outside the box is an allusion to a well-known puzzle where one has to connect nine dots, arranged in a square grid, with four straight lines drawn continuously without pen leaving paper.
The only solution to this puzzle is one where some of the lines extend beyond the border of the grid (or box). This puzzle was a popular gimmick among management consultants in the 1970s and 80s as a demonstration of the need to discard unwarranted assumptions (like the assumption that the lines must remain within the grid).
The term dates to at least to 1975 when it appears in the 14 July issue of Aviation Week and Space Technology:
We must step back and see if the solutions to our problems lie outside the box.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2015, by David Wilton