What is the first thing that should be attached to the individual before ascending or descending a fixed line?

In rope rescue operations, ensuring the safety of the individual during ascent or descent is paramount. The first thing to attach is a belay because it serves as a backup system. The belay device is designed to catch and hold the rope if the individual falls, thus preventing a potentially harmful drop. This method of safety is critical during both ascending and descending maneuvers on a fixed line.

While a harness is indeed important for proper fit and comfort, and a safety tether provides an additional layer of security to prevent separation from the anchor, the primary purpose of a belay is to take immediate action in the event of a fall. Ascender equipment may be used once the individual is safely secured with the belay in place, but the securing step that precedes it prioritizes fall protection. Therefore, starting with a belay ensures that the individual is protected as they begin their ascent or descent.