"I don't have the answer to your question, but I know if I'm elected, I'll appoint the brightest economic people I can find to solve the problem."
As opposed to other candidates who either talked along party lines and said they would tax the rich or give tax breaks to businesses and rich people.
I still feel like it was one of the most important things he said that got him elected. He never acted like he had all the answers.
When it comes to politics, a lot of people aren't looking to elect someone for their decision-making ability. They're looking to elect someone who is making the same decisions that they've made. For instance, people don't want a candidate who will "investigate whether universal healthcare is a good idea". The people have already decided whether or not it is, and they want someone who will agree with them.
In addition, not having a hardened position on something could mean that you intend to compromise with the opposition on that issue in order to appeal to more voters.
Qu'on me donne six lignes écrites de la main
du plus honnête homme, j'y trouverai de quoi
le faire pendre.
If you give me six lines written by the hand of
the most honest of men, I will find something in
them which will hang him.
-- Cardinal Richelieu (attributed)
One thing I realized very quickly while doing some volunteer work - when the guy in charge (or running to be in charge) says I do not know - people react as if they have lost all confidence in him/her despite understanding that not everyone can know everything.
so caveat emptor on preaching that.