Imagine for a moment that you’re seated in the front row of economy class. You just took off. As the plane climbs toward cruising altitude, through the curtains that separate you from the business-class cabin, you notice a dark, wet stain at the door of the toilet. You look closer. The stain is growing before your eyes. Is the toilet flooding? Oh dear. If you were visiting a friend’s house, or even just at a restaurant, you would say something to someone. So you press the attendant call button. By the time the seatbelt sign goes off, the stain has spread almost to your feet, and you’re wondering if your luggage is getting wet.