Milton Bradley has brought this into stark relief, but the problem has been going on as long as I've been alive. It's a sensitive topic, so I'll keep it short, easy on the sweet.
The following are true, albeit made up:
Cub fans are 85% more likely than other fans to believe they control the outcome of the game.
Cub fans are 77% more likely than other fans to think that a players looks significantly influence their on-field play.
Cub fans are three times as likely as Reds fans to blame a loss on a post-game press conference.
98% of Cubs fans have credited "supernatural forces" with the result of at least one entire Cubs season; of those, 89% believe they can control the aforementioned supernatural forces; 17% of Cub fans think those numbers are a little low.
86% of Cub fans are annoyed at baseball record keepers for not statistically tracking "clubhouse vibe."
2% of Cub fans are billy goats.
.01% of Cub fans were alive the last time they won a World Series.
100% of Cub fans who just read that winced.