In Western culture, “tying the knot” suggests the pledge of inseparable unity made by a married couple.
The expression comes from ancient India, when during the wedding ceremony the Hindu groom would put a brightly colored ribbon around the bride’s neck.
During the time it took to tie the ribbon into a knot, the bride’s father could demand a better price for his daughter, but once the knot was completed the bride became the groom’s forever.