A silver bullet, the quick, simple, solution to your number one problem. The thing that will kill the vampire. The only thing is that while you're searching for the silver bullet, which may not even exist, the solution that was always available was ignored. It was ignored because it looked too hard, too complicated, or required skills your organisation doesn't have right now. But most really difficult problems require those sorts of solutions. The kind of problem that can only be fixed by difficult work, investment, and adding new skills is a blessing. That kind of problem contains the gift of competitive advantage - because once you have cracked it, it remains hard for someone else to copy.
Inspired by Seth Godin's article on difficult problems.