What's luck got to do with it?By Dave Butler
Here it is in a nutshell: your hero can't win by luck, but all kinds of stuff can go wrong for him. In other words, your hero should be, if anything, unlucky.
Call this the Indiana Jones rule: he's lost his gun, the beam he's swinging from breaks, the grail slides further away from him in the earthquake, the girl hides in a basket only to be kidnapped when his back is turned. Bad luck is your friend -- it raises the stakes, it lengthens the odds against your hero and makes his eventual success even more satisfying, and it has comedic value. Good luck = bad writing; bad luck = writing gold.