A Brainteaser
Illustrate the problem

Nine points are disposed in a square on the game panel. You have to connect these 9 points with 4 straight lines (horizontal, vertical or diagonal) that can be drawn in one run, i.e. without interruption or lifting your pen from the game panel (and without returning).

Remember that you only have 4 straight line segments, and that all the points have to be connected!

Although it may seem incredible at first sight, there is a solution for this problem.

Once you have seen the solution, the fun is over. So, give it a thorough try before asking for the solution.

The Game Board
Go North
North indicator
Go North-East
North-East indicator
Go East
East indicator
Go South-East
South-East indicator
Go South
South indicator
Go South-West
South-West indicator
Go West
West indicator
Go North-West
North-West indicator
Click one of the points to indicate that it will be the starting point of the first segment.
Click a direction arrow on the dial to start drawing the first line segment in the chosen direction.
Click the same direction arrow to continue the line, or another arrow to start a new line segment.
You can not use a 5th line segment. Click the "Erase" button for another try.
You have used 4 line segments. Click the "Erase" button for another try or the "Solution" button.
Impossible to draw outside the game panel. Choose another direction, please.

You made it.

Nobody said you had to stay within the square formed by the 9 dots.
Click the "Erase" button if you want to try again.

Some Comments
I used this teaser (and some others) quite a number of times to illustrate courses about creativity, divergent or lateral thinking and conceptual frames.

Nine times out of ten, students react with a: It illustrates very clearly that self-imposed limitations or following common lines of thinking, can be important obstacles to find a solution.

As it "sells well", the Web offers a lot of information on divergent and lateral thinking. I just would like to mention two references: