Courtesy of Wikipedia:
Knitters use the term Sweater Curse or the Curse of the Love Sweater to describe a situation in which a knitter gives a hand-knit sweater to a significant other, who quickly breaks up with the knitter. In an alternative formulation, the relationship will end before the sweater is even completed. The belief is widely discussed in knitting publications and some knitters claim to have experienced the Sweater Curse; a recent poll indicated that 15% of active knitters say they have experienced the sweater curse firsthand, and 41% consider it a possibility that should be taken seriously.
Despite its name, the Sweater Curse is treated in knitting literature not as a superstition governed by paranormal forces, but rather as a real-world pitfall of knitting that has real-world explanations and solutions. Several plausible mechanisms for the sweater curse have been proposed, but it has not been studied systematically.
Have you experienced the Sweater Curse firsthand? Share your experiences in the comment section.