The sweater curse is a superstition that says if you knit or crochet a sweater for your romantic partner, your relationship will end soon after you give them the sweater.
It's not that the sweater itself is the cause of the break-up - it's more about the time and energy that goes into making a sweater. When you put that much effort into something, it can create a lot of pressure on the relationship.
Plus, if you're spending all your time crafting a sweater, you might not have as much time to spend with your partner. This can make them feel neglected or unimportant, which is not good for a relationship.
Of course, not everyone believes in the sweater curse, and many people have successfully knit sweaters for their partners without any negative consequences. But some people prefer not to take the risk, just in case.