how to do the 9 dot puzzle with 4 lines
The puzzle proposed an intellectual challenge -- to connect the dots by drawing four straight, continuous lines that pass through each of the nine dots, and never lifting the pencil from the paper. The conundrum is easily resolved, but only by drawing the lines outside the confines of the square area defined by the nine dots themselves. The phrase "thinking outside the box" is a restatement of the solution strategy. The puzzle only seems difficult because people commonly imagine a boundary around the edge of the dot array. The heart of the matter is the unspecified barrier that people typically perceive.