This video of Jacob Bronowski is possibly... one of the most elegant descriptions of what science and the pursuit of knowledge is really about. Including the admittance that with one argument a theory can be proven incorrect, and if we don't know the answer to something, that things are going to be alright. And that to have absolute truth, and faith in something is possibly more dangerous than any scientific research.
Why is it so hard to say 'I don't know' because when you really get down to it, that's what this is about... and if you 'know' then where's the fun in life?... there's nothing to learn anymore.