In social media you often find the worst advertisements. One that I saw recently is the following one. It was a video of a field with red and blue dots, and a toy figure going through the blue dot and removing them. The idea was that it should go through the grid of dots and remove all the blue dots in one go. One must not step back and go through a grid field where the blue dot was already removed. It showed a video with the figure failing to clear them all, leaving one.