I recently stumbled across the Reader’s Digest survey of Britain’s most trusted brands. One finding jumped out at me: the most trustworthy margarine is Flora. ‘I’ve never trusted a margarine,’ I thought. ‘I trust my doctor, my friends, my local policeman; not a margarine’. But the idea got me thinking. I do trust brands that I’m familiar with, that are of a consistently high quality and live up to promises. This trust represents a useful shorthand for the best choice in a world of increasing complexity. So I decided that I do indeed trust a margarine. I also trust a...