As I was standing in line at security at PDX on my way out to New Orleans, I happened to see Steve Novick, Democratic candidate for the US Senate seat currently held by Gordon Smith, in line ahead of me. I immediately noticed him because of the fact that he is very, very short. Now, we all know intuitively that height has absolutely nothing to do with the ability to be a good senator - or does it? Steve is obviously extremely intelligent, personable and hard working, so I would argue there is nothing innate about his height that lessens his ability to be an effective senator. But suppose I was worried about his ability to be elected not because of any prejudice I had about his height, but because I thought others might worry about the effect of his height. If everyone in Oregon were like me, personally not worried about his height but worried about others holding his height against him, notice what happens: my initial worry would be confirmed. No one would vote for him because of his height, not because they believed it made him less able but because they believed it would make him unelectable, and they would all have been proven right ex post. This is what in economics are known as self-fulfilling expectations: you expect his height to be a problem, so you act that way, and by such action you cause it to be true.
You can make a similar argument about his effectiveness once in the senate. A senator who is considering supporting him on some legislation he is proposing, might worry about his ability to drum up support among other senators, so decides not to - not because of his own ability, but because of how this senator believes others will act towards Novick. This worry causes the senator not to support Novick and thus causes his own worry to be shown to be correct.
So the punch line is that you can quite legitimately be worried about his height without believing that it has any effect on innate ability. But should you be? Notice that if everyone chose not to worry about what others might do, another equilibrium would result. An equilibrium where height played no role either in the election or in the senate. So what is a voter to do with such economic insight? Well, which equilibrium results really depends on how much you think other voters and senators will be influenced by height. Any one voter's marginal contribution to this is so small it is virtually meaningless, so an individual decision to disregard these concerns is not that meaningful in terms of outcomes, but may be meaningful in terms of one's own utility.