The absolute golden rule of scuba diving—the one that is drilled into every student from day one—is "Never hold your breath." In 2026, as in the early days of the sport, this rule remains non-negotiable because of the physics of lung over-expansion. As a diver ascends, the surrounding water pressure decreases, causing the compressed air inside the lungs to expand. If a diver holds their breath while moving upward, even by just a few feet, the expanding air can rupture the delicate lung tissue (pulmonary barotrauma), potentially leading to a fatal air embolism. Divers are taught to maintain a continuous, relaxed breathing rhythm at all times. Secondary "golden rules" include the "Rule of Thirds" for air management (one third for the way out, one third for the way back, and one third for emergencies) and the "Buddy System," which dictates that you should never dive alone. However, the requirement to keep the airway open during any change in depth is the most critical safety protocol in the entire diving world.