Bias

Approval and validation need to start from within. But (one way or another) you're always going to be biased, aren't you?

Signposts

Requirements are meant to be signposts. Guides. Help along the way. Never roadblocks.

Review and validation

Reviewing a deliverable - and validation of actions taken as a result of that review - should be done by the same person. Otherwise you risk a never-ending cycle of new change requests. And (and this is very important to the Facebook generation) you may never get your validation.