Outside the Box

In the figure below are 9 dots, which become a puzzle when we are asked to draw four straight, contiguous lines which will go through all 9 dots (or one contiguous line in four directions):

Typically, we are caught with one dot untouched - no matter where we start or how we move.  Our problem, you see, is that we made an assumption, namely that the dots constitute a box.  We think we are supposed to stay within the space "enclosed" by the dots.  Now this assumption is not part of the instructions at all.  We simply presumed it to be so - an unconscious "rule" we brought to the problem.  So we are at a loss to work the puzzle successfully.

Now, let's reverse the assumption.  The clue to the resolution is that instead of assuming we have to "stay inside" the box, the truth is that it is necessary to go outside the lines.  Once we make the reversed assumption, the puzzle is solvable in a matter of seconds.