I think for the Cubs it has just become a self-fulfilling prophecy. Kind of like with golf, if you approach the tee saying to yourself that you are going to duff the drive, you end up duffing the drive. There is so much pressure on the Cubs, and such an expectation that they will fail, I think plays a factor.
And on the flip side, build a history and tradition of winning, and it tends to work for you. The Yankees were the most storied team in baseball long before George Steinbrenner.
Of course, smart owners/management and boat-loads of money helps too.
If the Cubs were to Win it All, for the first time in ALL of our lifetimes, they would turn into , just another team in the NL Central .... unless the ownership stepped up big time to ensure that they would continue with top notch players.