Stripes on headphone jacks - You surely have noticed that all headphone jacks have 2 or 3 stripes on them. They aren’t made just for decoration: there are wires going to both headphones from every stripe, and if they weren’t there, you would only hear sound coming from one of the headphones. Dimples on golf balls - The first golf balls were smooth. With time, however, golf players realized by trial and error that the balls with the best properties were old, scuffed, and cracked ones. So, they kept using the same old balls for years. Manufacturers noticed this tendency and started producing artificially aged dimpled balls. Notebook margins - The original reason for margins was to provide a space where a teacher could write her comments.The truth is that books in the past often fell victim to mice and rats who liked to gnaw on paper. In order not to let the rodents eat parts of information along with the paper, people started to leave empty spaces at the edges,