The idea of a "red thread" is a metaphor that appears in various cultures and contexts, symbolizing connection, guiding principles, or destiny. Here are a few notable origins and uses:

1. Chinese Mythology: In Chinese culture, the "red thread of fate" is a belief originating from an ancient Chinese legend. According to the myth, the gods tie an invisible red thread around the ankles of those destined to meet or help each other in a certain way. This thread may stretch or tangle but will never break. It's often associated with the destined love between two people.

2. Greek Mythology: The concept is somewhat mirrored in Greek mythology through the story of Theseus and Ariadne. After killing the beast, Ariadne gives Theseus a ball of red thread to find his way out of the Minotaur's labyrinth. Here, the red thread symbolizes guidance and ingenuity.

3. Nordic Mythology: In Norse mythology, the Norns, the goddesses of destiny, weave the fate of all beings. Their thread of life can be seen metaphorically as a red thread that determines the lifelines of all individuals.

4. General Usage: Beyond these cultural references, the idea of a red thread has been used more broadly to symbolize a common theme, connection, or guiding principle throughout a story, idea, or project. It represents the underlying continuity or the central theme that connects various elements.

These "red thread" metaphors share a common theme of connectivity, whether through fate, destiny, guidance, or thematic linkage. As such, The Red Thread are using this concept in the context of relationships for gay men, which is about finding connectivity for intimacy, friendship, partnership, and spirituality.