Apple has decided with Final Cut Pro X that you should see all projects all the time in the interface. Some people don't like that. Say for example you edit training videos for two rival companies. It's okay for you so see the proprietary stuff but it's not really the best idea to let one company know you're working for their rival as well.
So, Apple has revealed how to "hide" (remove) a project (event) in Final Cut Pro X. They posted a document about just this one issue here.
Basically you move a project's media (event) from the folder Final Cut Pro X looks in to find events to another folder so Final Cut Pro X just doesn't see it. It's like hiding your car keys in the sun visor.
How hard would it be to add a Visibility Toggle or something within Final Cut Pro X? I mean really.