Stockholm syndrome is named after the Norrmalmstorg robbery of Kreditbanken at Norrmalmstorg in Stockholm, Sweden, in which several bank employees were held hostage in a bank vault from August 23 to August 28, 1973. During this situation, the victims became emotionally attached to their captors. That’s the official version (Wikipedia).
Here is a better version. Stockholm is captivating. Stay there for a few days and feel how you developing attachment to this calm and beautiful city, calm and beautiful people, and even to its ever changing weather. They called it Stockholm Syndrome for a reason.