When printing, it happens from time to time that a print job fails, and this blocks all subsequent jobs. By default, this problem can be solved from the print queue.
Few users have a printer with a so-called duplex unit that can print on both sides. This is typically a feature that is specific to more expensive models, perhaps intended for a corporate environment and is rarely added to the average home printer. With a little trickery, you can still produce such a print – though in two steps.