I love this passage by Paul Mason in the introduction to The Global Minotaur:
Most politicians cannot be theorists. First, because they are rarely thinkers; second, because the frenetic lifestyle they impose on themselves leaves no time for big ideas. But most of all because to be a theorist you have to admit the possibility of being wrong –the provisionality of knowledge –and you know you cannot spin your way out of a theoretical problem.
Mark Carrigan 