You have one if/then statement to give a robot, it will repeatedly follow this instruction. The robot is on an infinite expanse of tiles, it can see if it has been to the square it is on or is trying to go to before, what 1 if/then statement carried out over and over again will have the robot visit every tile (the robot has no memory, so it can not refer to previous events)
It doesn’t HAVE to be an if/then statement, it is possible to achieve the same result with a normal rule, but it is easier to think about an if/then statement