9. Kurt Angle Joins The Alliance
The WCW Invasion storyline was a complete mess. The WCW stars were made to look inferior to their WWF counterparts, and while there were some high-profile defections from the WWF to The Alliance, they basically served to hammer home the fact that WWE management felt the WCW side needed those guys for "star power."
That is a reason, though, which is more than can be said for Kurt Angle's defection.
During the Invasion, Angle turned face for the first time and emerged as the top hero on the WWE side. After winning both the WCW and WWF titles for his company and his country, though, he turned on Vince McMahon and attacked fellow WWF superstars with a chair, becoming part of the group he had viciously fought.
Thankfully, the WWF made the best out of a bad situation - during the winner-take-all match at Survivor Series, Angle helped the WWF claim victory, claiming to have been a mole (a claim which was doubted by Edge, who said Angle was probably just helping whichever side looked like it was going to win).
Despite the elegant ending, though, Angle's initial turn felt like a bad swerve in a period full of them, and it's not hard to imagine that nothing past his attack was planned at first.