In a somewhat recent article I addressed reasons curses fail. Here's an example of a successful curse that worked as intended, being part of a large scale magical endeavor.
Some years back I embarked on a magical crusade with Mr. Farrell. The campaign started off with a bang, only to peter out because someone later forgot to play Christopher Columbus thus not leaving room for someone else to play Caesar. But at least the first stage was glorious. Its strategic aim was to permanently separate a couple.
Yours truly fulfilled the task with flying colors, but received no medal or promotion afterwards. At any rate, a powerful descending Saturn in domicile and triplicity did the job in no time. Iartă-mă, Dovlecel, but I was ever only thinking of your long-term well-being!