What is the primary reason for using a figure eight knot?

The primary reason for using a figure-eight knot is to create a secure loop. This knot is known for its reliability and strength, making it an essential choice in various applications, particularly in climbing, rescue operations, and firefighting. The structure of the figure-eight creates a loop that is less likely to slip or come undone under tension, providing a strong anchor point.

While it is also true that the figure-eight knot can be used to join two ropes and has other applications, its most recognized and critical purpose is to form a stable loop at the end of a rope. This loop can be used for securing items, attaching to harnesses, or anchoring in rescue scenarios. Its ease of tying and untieing, even after being subjected to heavy loads, further emphasizes its utility for creating secure loops in practical situations.