Capsule: a horrific collision between the immovable GM preparation and the irresistible PC creation phase.
The Story: My college gaming group had been playing Champions out of the Big Blue Book like nobody's business, sometimes even two campaigns at once. But fantasy had been dying off as the 2nd Edition of D&D was really beginning to show its age and so many new games were coming onto the market. The fantasy genre still had its fans in our gaming group, and when Fantasy Hero came out Andrew saw a chance to take a popular game system and meld it to a fantasy book series he really enjoyed. And for the life of me I can not remember the series, except that it was this high fantasy that takes place in historical Europe complete with the Christian Church and this family of people with magical/psychic powers and some such thing. Andrew went all out on the planning, compiling a huge three-ring binder of material detailing the culture and background of the campaign, even composing poetry.
The gaming group, on the other hand, just went ahead and created the archtypical motley crew of random fantasy tropes: a sorceress, a barbarian with a giant axe, a waifish pickpocketing thief, etc. We were even proud of ourselves that we concocted this elaborate backstory where we were all actually members of the same family, mostly siblings. This backstory was completely independent of the background and tone of what the GM had created. Disheartened, Andrew never bothered even running a single session, but gave up and moved on.
I read a lot about campaign preparation nowadays, especially the tension between having the players have so much input they are essentially co-creators, to the other side of the philosophical spectrum where GM's suggest that the players should respect and trust them enough to go with what they want to run. It's too bad, because Andrew might have enjoyed exploring what the players had created, and vice versa, if only they had been willing to come together more, and I'd have actually seen how Fantasy Hero played.