Scott Berkun has a collection of essays including a great one on Why smart people defend bad ideas. It’s certainly something I’ve done before to my detriment and it is something I’ve seen in others that I’ve tried (and failed) to avoid.
The problem with smart people is that they like to be right and sometimes will defend ideas to the death rather than admit they’re wrong. This is bad. Worse, if they got away with it when they were young (say, because they were smarter than their parents, their friends, and their parent’s friends) they’ve probably built an ego around being right, and will therefore defend their perfect record of invented righteousness to the death. Smart people often fall into the trap of preferring to be right even if it’s based in delusion, or results in them, or their loved ones, becoming miserable.